/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#include "mongo/platform/basic.h"

#include "mongo/bson/bsonmisc.h"
#include "mongo/config.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/json.h"
#include "mongo/db/pipeline/accumulator.h"
#include "mongo/db/pipeline/document.h"
#include "mongo/db/pipeline/document_value_test_util.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/expression_context_for_test.h"
#include "mongo/db/pipeline/value_comparator.h"
#include "mongo/db/query/collation/collator_interface_mock.h"
#include "mongo/dbtests/dbtests.h"
#include "mongo/unittest/unittest.h"

namespace ExpressionTests {

using boost::intrusive_ptr;
using std::initializer_list;
using std::numeric_limits;
using std::pair;
using std::set;
using std::sort;
using std::string;
using std::vector;
using std::list;

/**
 * Creates an expression given by 'expressionName' and evaluates it using
 * 'operands' as inputs, returning the result.
 */
static Value evaluateExpression(const string& expressionName,
                                const vector<ImplicitValue>& operands) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    const BSONObj obj = BSON(expressionName << ImplicitValue::convertToValue(operands));
    auto expression = Expression::parseExpression(expCtx, obj, vps);
    Value result = expression->evaluate(Document());
    return result;
}

/**
 * Creates an expression which parses named arguments via an object specification, then evaluates it
 * and returns the result.
 */
static Value evaluateNamedArgExpression(const string& expressionName, const Document& operand) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    const BSONObj obj = BSON(expressionName << operand);
    auto expression = Expression::parseExpression(expCtx, obj, vps);
    Value result = expression->evaluate(Document());
    return result;
}

/**
 * Takes the name of an expression as its first argument and a list of pairs of arguments and
 * expected results as its second argument, and asserts that for the given expression the arguments
 * evaluate to the expected results.
 */
static void assertExpectedResults(
    const string& expression,
    initializer_list<pair<vector<ImplicitValue>, ImplicitValue>> operations) {
    for (auto&& op : operations) {
        try {
            Value result = evaluateExpression(expression, op.first);
            ASSERT_VALUE_EQ(op.second, result);
            ASSERT_EQUALS(op.second.getType(), result.getType());
        } catch (...) {
            log() << "failed with arguments: " << ImplicitValue::convertToValue(op.first);
            throw;
        }
    }
}

/** Convert BSONObj to a BSONObj with our $const wrappings. */
static BSONObj constify(const BSONObj& obj, bool parentIsArray = false) {
    BSONObjBuilder bob;
    for (BSONObjIterator itr(obj); itr.more(); itr.next()) {
        BSONElement elem = *itr;
        if (elem.type() == Object) {
            bob << elem.fieldName() << constify(elem.Obj(), false);
        } else if (elem.type() == Array && !parentIsArray) {
            // arrays within arrays are treated as constant values by the real
            // parser
            bob << elem.fieldName() << BSONArray(constify(elem.Obj(), true));
        } else if (elem.fieldNameStringData() == "$const" ||
                   (elem.type() == mongo::String && elem.valueStringDataSafe().startsWith("$"))) {
            bob.append(elem);
        } else {
            bob.append(elem.fieldName(), BSON("$const" << elem));
        }
    }
    return bob.obj();
}

/** Check binary equality, ensuring use of the same numeric types. */
static void assertBinaryEqual(const BSONObj& expected, const BSONObj& actual) {
    ASSERT_BSONOBJ_EQ(expected, actual);
    ASSERT(expected.binaryEqual(actual));
}

/** Convert Value to a wrapped BSONObj with an empty string field name. */
static BSONObj toBson(const Value& value) {
    BSONObjBuilder bob;
    value.addToBsonObj(&bob, "");
    return bob.obj();
}

/** Convert Expression to BSON. */
static BSONObj expressionToBson(const intrusive_ptr<Expression>& expression) {
    return BSON("" << expression->serialize(false)).firstElement().embeddedObject().getOwned();
}

/** Convert Document to BSON. */
static BSONObj toBson(const Document& document) {
    return document.toBson();
}

/** Create a Document from a BSONObj. */
Document fromBson(BSONObj obj) {
    return Document(obj);
}

/** Create a Value from a BSONObj. */
Value valueFromBson(BSONObj obj) {
    BSONElement element = obj.firstElement();
    return Value(element);
}

template <typename T>
intrusive_ptr<ExpressionConstant> makeConstant(T&& val) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    return ExpressionConstant::create(expCtx, Value(std::forward<T>(val)));
}

class ExpressionBaseTest : public unittest::Test {
public:
    void addOperand(intrusive_ptr<ExpressionNary> expr, Value arg) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        expr->addOperand(ExpressionConstant::create(expCtx, arg));
    }
};

class ExpressionNaryTestOneArg : public ExpressionBaseTest {
public:
    virtual void assertEvaluates(Value input, Value output) {
        addOperand(_expr, input);
        ASSERT_VALUE_EQ(output, _expr->evaluate(Document()));
        ASSERT_EQUALS(output.getType(), _expr->evaluate(Document()).getType());
    }

    intrusive_ptr<ExpressionNary> _expr;
};

class ExpressionNaryTestTwoArg : public ExpressionBaseTest {
public:
    virtual void assertEvaluates(Value input1, Value input2, Value output) {
        addOperand(_expr, input1);
        addOperand(_expr, input2);
        ASSERT_VALUE_EQ(output, _expr->evaluate(Document()));
        ASSERT_EQUALS(output.getType(), _expr->evaluate(Document()).getType());
    }

    intrusive_ptr<ExpressionNary> _expr;
};

/* ------------------------- NaryExpression -------------------------- */

/** A dummy child of ExpressionNary used for testing. */
class Testable : public ExpressionNary {
public:
    virtual Value evaluate(const Document& root) const {
        // Just put all the values in a list.
        // By default, this is not associative/commutative so the results will change if
        // instantiated as commutative or associative and operations are reordered.
        vector<Value> values;
        for (auto&& child : _children)
            values.push_back(child->evaluate(root));
        return Value(values);
    }

    virtual const char* getOpName() const {
        return "$testable";
    }

    virtual bool isAssociative() const {
        return _isAssociative;
    }

    virtual bool isCommutative() const {
        return _isCommutative;
    }

    void acceptVisitor(ExpressionVisitor* visitor) final {
        return visitor->visit(this);
    }

    static intrusive_ptr<Testable> create(bool associative, bool commutative) {
        return new Testable(associative, commutative);
    }

private:
    Testable(bool isAssociative, bool isCommutative)
        : ExpressionNary(
              boost::intrusive_ptr<ExpressionContextForTest>(new ExpressionContextForTest())),
          _isAssociative(isAssociative),
          _isCommutative(isCommutative) {}
    bool _isAssociative;
    bool _isCommutative;
};

class ExpressionNaryTest : public unittest::Test {
public:
    virtual void setUp() override {
        _notAssociativeNorCommutative = Testable::create(false, false);
        _associativeOnly = Testable::create(true, false);
        _associativeAndCommutative = Testable::create(true, true);
    }

protected:
    void assertDependencies(const intrusive_ptr<Testable>& expr,
                            const BSONArray& expectedDependencies) {
        DepsTracker dependencies;
        expr->addDependencies(&dependencies);
        BSONArrayBuilder dependenciesBson;
        for (set<string>::const_iterator i = dependencies.fields.begin();
             i != dependencies.fields.end();
             ++i) {
            dependenciesBson << *i;
        }
        ASSERT_BSONOBJ_EQ(expectedDependencies, dependenciesBson.arr());
        ASSERT_EQUALS(false, dependencies.needWholeDocument);
        ASSERT_EQUALS(false, dependencies.getNeedsMetadata(DepsTracker::MetadataType::TEXT_SCORE));
    }

    void assertContents(const intrusive_ptr<Testable>& expr, const BSONArray& expectedContents) {
        ASSERT_BSONOBJ_EQ(constify(BSON("$testable" << expectedContents)), expressionToBson(expr));
    }

    void addOperandArrayToExpr(const intrusive_ptr<Testable>& expr, const BSONArray& operands) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        VariablesParseState vps = expCtx->variablesParseState;
        BSONObjIterator i(operands);
        while (i.more()) {
            BSONElement element = i.next();
            expr->addOperand(Expression::parseOperand(expCtx, element, vps));
        }
    }

    intrusive_ptr<Testable> _notAssociativeNorCommutative;
    intrusive_ptr<Testable> _associativeOnly;
    intrusive_ptr<Testable> _associativeAndCommutative;
};

TEST_F(ExpressionNaryTest, AddedConstantOperandIsSerialized) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    _notAssociativeNorCommutative->addOperand(ExpressionConstant::create(expCtx, Value(9)));
    assertContents(_notAssociativeNorCommutative, BSON_ARRAY(9));
}

TEST_F(ExpressionNaryTest, AddedFieldPathOperandIsSerialized) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    _notAssociativeNorCommutative->addOperand(ExpressionFieldPath::create(expCtx, "ab.c"));
    assertContents(_notAssociativeNorCommutative, BSON_ARRAY("$ab.c"));
}

TEST_F(ExpressionNaryTest, ValidateEmptyDependencies) {
    assertDependencies(_notAssociativeNorCommutative, BSONArray());
}

TEST_F(ExpressionNaryTest, ValidateConstantExpressionDependency) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    _notAssociativeNorCommutative->addOperand(ExpressionConstant::create(expCtx, Value(1)));
    assertDependencies(_notAssociativeNorCommutative, BSONArray());
}

TEST_F(ExpressionNaryTest, ValidateFieldPathExpressionDependency) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    _notAssociativeNorCommutative->addOperand(ExpressionFieldPath::create(expCtx, "ab.c"));
    assertDependencies(_notAssociativeNorCommutative, BSON_ARRAY("ab.c"));
}

TEST_F(ExpressionNaryTest, ValidateObjectExpressionDependency) {
    BSONObj spec = BSON("" << BSON("a"
                                   << "$x"
                                   << "q"
                                   << "$r"));
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    BSONElement specElement = spec.firstElement();
    VariablesParseState vps = expCtx->variablesParseState;
    _notAssociativeNorCommutative->addOperand(
        Expression::parseObject(expCtx, specElement.Obj(), vps));
    assertDependencies(_notAssociativeNorCommutative,
                       BSON_ARRAY("r"
                                  << "x"));
}

TEST_F(ExpressionNaryTest, SerializationToBsonObj) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    _notAssociativeNorCommutative->addOperand(ExpressionConstant::create(expCtx, Value(5)));
    ASSERT_BSONOBJ_EQ(BSON("foo" << BSON("$testable" << BSON_ARRAY(BSON("$const" << 5)))),
                      BSON("foo" << _notAssociativeNorCommutative->serialize(false)));
}

TEST_F(ExpressionNaryTest, SerializationToBsonArr) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    _notAssociativeNorCommutative->addOperand(ExpressionConstant::create(expCtx, Value(5)));
    ASSERT_BSONOBJ_EQ(constify(BSON_ARRAY(BSON("$testable" << BSON_ARRAY(5)))),
                      BSON_ARRAY(_notAssociativeNorCommutative->serialize(false)));
}

// Verify that the internal operands are optimized
TEST_F(ExpressionNaryTest, InternalOperandOptimizationIsDone) {
    BSONArray spec = BSON_ARRAY(BSON("$and" << BSONArray()) << "$abc");
    addOperandArrayToExpr(_notAssociativeNorCommutative, spec);
    assertContents(_notAssociativeNorCommutative, spec);
    ASSERT(_notAssociativeNorCommutative == _notAssociativeNorCommutative->optimize());
    assertContents(_notAssociativeNorCommutative, BSON_ARRAY(true << "$abc"));
}

// Verify that if all the operands are constants, the expression is replaced
// by a constant value equivalent to the expression applied to the operands.
TEST_F(ExpressionNaryTest, AllConstantOperandOptimization) {
    BSONArray spec = BSON_ARRAY(1 << 2);
    addOperandArrayToExpr(_notAssociativeNorCommutative, spec);
    assertContents(_notAssociativeNorCommutative, spec);
    intrusive_ptr<Expression> optimized = _notAssociativeNorCommutative->optimize();
    ASSERT(_notAssociativeNorCommutative != optimized);
    ASSERT_BSONOBJ_EQ(BSON("$const" << BSON_ARRAY(1 << 2)), expressionToBson(optimized));
}

// Verify that the optimization of grouping constant and non-constant operands
// and then applying the expression to the constant operands to reduce them to
// one constant operand is only applied if the expression is associative and
// commutative.
TEST_F(ExpressionNaryTest, GroupingOptimizationOnNotCommutativeNorAssociative) {
    BSONArray spec = BSON_ARRAY(55 << 66 << "$path");
    addOperandArrayToExpr(_notAssociativeNorCommutative, spec);
    assertContents(_notAssociativeNorCommutative, spec);
    intrusive_ptr<Expression> optimized = _notAssociativeNorCommutative->optimize();
    ASSERT(_notAssociativeNorCommutative == optimized);
    assertContents(_notAssociativeNorCommutative, spec);
}

TEST_F(ExpressionNaryTest, GroupingOptimizationOnAssociativeOnlyFrontOperands) {
    BSONArray spec = BSON_ARRAY(55 << 66 << "$path");
    addOperandArrayToExpr(_associativeOnly, spec);
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);
    assertContents(_associativeOnly, BSON_ARRAY(BSON_ARRAY(55 << 66) << "$path"));
}

TEST_F(ExpressionNaryTest, GroupingOptimizationOnAssociativeOnlyMiddleOperands) {
    BSONArray spec = BSON_ARRAY("$path1" << 55 << 66 << "$path");
    addOperandArrayToExpr(_associativeOnly, spec);
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);
    assertContents(_associativeOnly, BSON_ARRAY("$path1" << BSON_ARRAY(55 << 66) << "$path"));
}

TEST_F(ExpressionNaryTest, GroupingOptimizationOnAssociativeOnlyBackOperands) {
    BSONArray spec = BSON_ARRAY("$path" << 55 << 66);
    addOperandArrayToExpr(_associativeOnly, spec);
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);
    assertContents(_associativeOnly, BSON_ARRAY("$path" << BSON_ARRAY(55 << 66)));
}

TEST_F(ExpressionNaryTest, GroupingOptimizationOnAssociativeOnlyNotExecuteOnSingleConstantsFront) {
    BSONArray spec = BSON_ARRAY(55 << "$path");
    addOperandArrayToExpr(_associativeOnly, spec);
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);
    assertContents(_associativeOnly, BSON_ARRAY(55 << "$path"));
}

TEST_F(ExpressionNaryTest, GroupingOptimizationOnAssociativeOnlyNotExecuteOnSingleConstantsMiddle) {
    BSONArray spec = BSON_ARRAY("$path1" << 55 << "$path2");
    addOperandArrayToExpr(_associativeOnly, spec);
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);
    assertContents(_associativeOnly, BSON_ARRAY("$path1" << 55 << "$path2"));
}

TEST_F(ExpressionNaryTest, GroupingOptimizationOnAssociativeOnlyNotExecuteOnSingleConstantsBack) {
    BSONArray spec = BSON_ARRAY("$path" << 55);
    addOperandArrayToExpr(_associativeOnly, spec);
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);
    assertContents(_associativeOnly, BSON_ARRAY("$path" << 55));
}

TEST_F(ExpressionNaryTest, GroupingOptimizationOnCommutativeAndAssociative) {
    BSONArray spec = BSON_ARRAY(55 << 66 << "$path");
    addOperandArrayToExpr(_associativeAndCommutative, spec);
    assertContents(_associativeAndCommutative, spec);
    intrusive_ptr<Expression> optimized = _associativeAndCommutative->optimize();
    ASSERT(_associativeAndCommutative == optimized);
    assertContents(_associativeAndCommutative, BSON_ARRAY("$path" << BSON_ARRAY(55 << 66)));
}

TEST_F(ExpressionNaryTest, FlattenOptimizationNotDoneOnOtherExpressionsForAssociativeExpressions) {
    BSONArray spec = BSON_ARRAY(66 << "$path" << BSON("$sum" << BSON_ARRAY("$path" << 2)));
    addOperandArrayToExpr(_associativeOnly, spec);
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);
    assertContents(_associativeOnly, spec);
}

TEST_F(ExpressionNaryTest, FlattenOptimizationNotDoneOnSameButNotAssociativeExpression) {
    BSONArrayBuilder specBuilder;

    intrusive_ptr<Testable> innerOperand = Testable::create(false, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1" << 101));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(99 << "$path2"));
    specBuilder << 99 << "$path2";

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    assertContents(_associativeOnly, spec);
}

// Test that if there is an expression of the same type in a non-commutative nor associative
// expression, the inner expression is not expanded.
// {"$testable" : [ { "$testable" : [ 100, "$path1"] }, 99, "$path2"] } is optimized to:
// {"$testable" : [ { "$testable" : [ 100, "$path1"] }, 99, "$path2"] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnNotCommutativeNorAssociative) {
    BSONArrayBuilder specBuilder;

    intrusive_ptr<Testable> innerOperand = Testable::create(false, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1"));
    specBuilder.append(expressionToBson(innerOperand));
    _notAssociativeNorCommutative->addOperand(innerOperand);

    addOperandArrayToExpr(_notAssociativeNorCommutative, BSON_ARRAY(99 << "$path2"));
    specBuilder << 99 << "$path2";

    BSONArray spec = specBuilder.arr();
    assertContents(_notAssociativeNorCommutative, spec);
    intrusive_ptr<Expression> optimized = _notAssociativeNorCommutative->optimize();
    ASSERT(_notAssociativeNorCommutative == optimized);

    assertContents(_notAssociativeNorCommutative, spec);
}

// Test that if there is an expression of the same type as the first operand
// in a non-commutative but associative expression, the inner expression is expanded.
// Also, there shouldn't be any grouping of the operands.
// {"$testable" : [ { "$testable" : [ 100, "$path1"] }, 99, "$path2"] } is optimized to:
// {"$testable" : [ 100, "$path1", 99, "$path2"] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnAssociativeOnlyFrontOperandNoGroup) {
    BSONArrayBuilder specBuilder;

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1"));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(99 << "$path2"));
    specBuilder << 99 << "$path2";

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent = BSON_ARRAY(100 << "$path1" << 99 << "$path2");
    assertContents(_associativeOnly, expectedContent);
}

// Test that if there is an expression of the same type as the first operand
// in a non-commutative but associative expression, the inner expression is expanded.
// Partial collapsing optimization should be applied to the operands.
// {"$testable" : [ { "$testable" : [ 100, "$path1", 101] }, 99, "$path2"] } is optimized to:
// {"$testable" : [ 100, "$path1", [101, 99], "$path2"] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnAssociativeOnlyFrontOperandAndGroup) {
    BSONArrayBuilder specBuilder;

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1" << 101));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(99 << "$path2"));
    specBuilder << 99 << "$path2";

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent = BSON_ARRAY(100 << "$path1" << BSON_ARRAY(101 << 99) << "$path2");
    assertContents(_associativeOnly, expectedContent);
}

// Test that if there is an expression of the same type in the middle of the operands
// in a non-commutative but associative expression, the inner expression is expanded.
// Partial collapsing optimization should not be applied to the operands.
// {"$testable" : [ 200, "$path3", { "$testable" : [ 100, "$path1"] }, 99, "$path2"] } is
// optimized to: {"$testable" : [ 200, "$path3", 100, "$path1", 99, "$path2"] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnAssociativeOnlyMiddleOperandNoGroup) {
    BSONArrayBuilder specBuilder;

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(200 << "$path3"));
    specBuilder << 200 << "$path3";

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1"));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(99 << "$path2"));
    specBuilder << 99 << "$path2";

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent = BSON_ARRAY(200 << "$path3" << 100 << "$path1" << 99 << "$path2");
    assertContents(_associativeOnly, expectedContent);
}

// Test that if there is an expression of the same type in the middle of the operands
// in a non-commutative but associative expression, the inner expression is expanded.
// Partial collapsing optimization should be applied to the operands.
// {"$testable" : [ 200, "$path3", 201 { "$testable" : [ 100, "$path1", 101] }, 99, "$path2"] } is
// optimized to: {"$testable" : [ 200, "$path3", [201, 100], "$path1", [101, 99], "$path2"] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnAssociativeOnlyMiddleOperandAndGroup) {
    BSONArrayBuilder specBuilder;

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(200 << "$path3" << 201));
    specBuilder << 200 << "$path3" << 201;

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1" << 101));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(99 << "$path2"));
    specBuilder << 99 << "$path2";

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent = BSON_ARRAY(
        200 << "$path3" << BSON_ARRAY(201 << 100) << "$path1" << BSON_ARRAY(101 << 99) << "$path2");
    assertContents(_associativeOnly, expectedContent);
}

// Test that if there is an expression of the same type in the back of the operands in a
// non-commutative but associative expression, the inner expression is expanded.
// Partial collapsing optimization should not be applied to the operands.
// {"$testable" : [ 200, "$path3", { "$testable" : [ 100, "$path1"] }] } is
// optimized to: {"$testable" : [ 200, "$path3", 100, "$path1"] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnAssociativeOnlyBackOperandNoGroup) {
    BSONArrayBuilder specBuilder;

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(200 << "$path3"));
    specBuilder << 200 << "$path3";

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1"));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent = BSON_ARRAY(200 << "$path3" << 100 << "$path1");
    assertContents(_associativeOnly, expectedContent);
}

// Test that if there is an expression of the same type in the back of the operands in a
// non-commutative but associative expression, the inner expression is expanded.
// Partial collapsing optimization should be applied to the operands.
// {"$testable" : [ 200, "$path3", 201, { "$testable" : [ 100, "$path1", 101] }] } is
// optimized to: {"$testable" : [ 200, "$path3", [201, 100], "$path1", 101] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnAssociativeOnlyBackOperandAndGroup) {
    BSONArrayBuilder specBuilder;

    addOperandArrayToExpr(_associativeOnly, BSON_ARRAY(200 << "$path3" << 201));
    specBuilder << 200 << "$path3" << 201;

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1" << 101));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent =
        BSON_ARRAY(200 << "$path3" << BSON_ARRAY(201 << 100) << "$path1" << 101);
    assertContents(_associativeOnly, expectedContent);
}

// Test that if there are two consecutive inner expressions of the same type in a non-commutative
// but associative expression, both expressions are correctly flattened.
// Partial collapsing optimization should not be applied to the operands.
// {"$testable" : [ { "$testable" : [ 100, "$path1"] }, { "$testable" : [ 200, "$path2"] }] } is
// optimized to: {"$testable" : [ 100, "$path1", 200, "$path2"] }
TEST_F(ExpressionNaryTest, FlattenConsecutiveInnerOperandsOptimizationOnAssociativeOnlyNoGroup) {
    BSONArrayBuilder specBuilder;

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1"));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    intrusive_ptr<Testable> innerOperand2 = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand2, BSON_ARRAY(200 << "$path2"));
    specBuilder.append(expressionToBson(innerOperand2));
    _associativeOnly->addOperand(innerOperand2);

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent = BSON_ARRAY(100 << "$path1" << 200 << "$path2");
    assertContents(_associativeOnly, expectedContent);
}

// Test that if there are two consecutive inner expressions of the same type in a non-commutative
// but associative expression, both expressions are correctly flattened.
// Partial collapsing optimization should be applied to the operands.
// {"$testable" : [ { "$testable" : [ 100, "$path1", 101] }, { "$testable" : [ 200, "$path2"] }] }
// is optimized to: {"$testable" : [ 100, "$path1", [ 101, 200], "$path2"] }
TEST_F(ExpressionNaryTest, FlattenConsecutiveInnerOperandsOptimizationOnAssociativeAndGroup) {
    BSONArrayBuilder specBuilder;

    intrusive_ptr<Testable> innerOperand = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1" << 101));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeOnly->addOperand(innerOperand);

    intrusive_ptr<Testable> innerOperand2 = Testable::create(true, false);
    addOperandArrayToExpr(innerOperand2, BSON_ARRAY(200 << "$path2"));
    specBuilder.append(expressionToBson(innerOperand2));
    _associativeOnly->addOperand(innerOperand2);

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeOnly, spec);
    intrusive_ptr<Expression> optimized = _associativeOnly->optimize();
    ASSERT(_associativeOnly == optimized);

    BSONArray expectedContent = BSON_ARRAY(100 << "$path1" << BSON_ARRAY(101 << 200) << "$path2");
    assertContents(_associativeOnly, expectedContent);
}

// Test that inner expressions are correctly flattened and constant operands re-arranged and
// collapsed when using a commutative and associative expression.
// {"$testable" : [ 200, "$path3", 201, { "$testable" : [ 100, "$path1", 101] }, 99, "$path2"] } is
// optimized to: {"$testable" : [ "$path3", "$path1", "$path2", [200, 201, [ 100, 101], 99] ] }
TEST_F(ExpressionNaryTest, FlattenInnerOperandsOptimizationOnCommutativeAndAssociative) {
    BSONArrayBuilder specBuilder;

    addOperandArrayToExpr(_associativeAndCommutative, BSON_ARRAY(200 << "$path3" << 201));
    specBuilder << 200 << "$path3" << 201;

    intrusive_ptr<Testable> innerOperand = Testable::create(true, true);
    addOperandArrayToExpr(innerOperand, BSON_ARRAY(100 << "$path1" << 101));
    specBuilder.append(expressionToBson(innerOperand));
    _associativeAndCommutative->addOperand(innerOperand);

    addOperandArrayToExpr(_associativeAndCommutative, BSON_ARRAY(99 << "$path2"));
    specBuilder << 99 << "$path2";

    BSONArray spec = specBuilder.arr();
    assertContents(_associativeAndCommutative, spec);
    intrusive_ptr<Expression> optimized = _associativeAndCommutative->optimize();
    ASSERT(_associativeAndCommutative == optimized);

    BSONArray expectedContent = BSON_ARRAY("$path3"
                                           << "$path1"
                                           << "$path2"
                                           << BSON_ARRAY(200 << 201 << BSON_ARRAY(100 << 101)
                                                             << 99));
    assertContents(_associativeAndCommutative, expectedContent);
}

/* ------------------------- ExpressionArrayToObject -------------------------- */

TEST(ExpressionArrayToObjectTest, KVFormatSimple) {
    assertExpectedResults("$arrayToObject",
                          {{{Value(BSON_ARRAY(BSON("k"
                                                   << "key1"
                                                   << "v"
                                                   << 2)
                                              << BSON("k"
                                                      << "key2"
                                                      << "v"
                                                      << 3)))},
                            {Value(BSON("key1" << 2 << "key2" << 3))}}});
}

TEST(ExpressionArrayToObjectTest, KVFormatWithDuplicates) {
    assertExpectedResults("$arrayToObject",
                          {{{Value(BSON_ARRAY(BSON("k"
                                                   << "hi"
                                                   << "v"
                                                   << 2)
                                              << BSON("k"
                                                      << "hi"
                                                      << "v"
                                                      << 3)))},
                            {Value(BSON("hi" << 3))}}});
}

TEST(ExpressionArrayToObjectTest, ListFormatSimple) {
    assertExpectedResults("$arrayToObject",
                          {{{Value(BSON_ARRAY(BSON_ARRAY("key1" << 2) << BSON_ARRAY("key2" << 3)))},
                            {Value(BSON("key1" << 2 << "key2" << 3))}}});
}

TEST(ExpressionArrayToObjectTest, ListFormWithDuplicates) {
    assertExpectedResults("$arrayToObject",
                          {{{Value(BSON_ARRAY(BSON_ARRAY("key1" << 2) << BSON_ARRAY("key1" << 3)))},
                            {Value(BSON("key1" << 3))}}});
}

/* ------------------------- ExpressionCeil -------------------------- */

class ExpressionCeilTest : public ExpressionNaryTestOneArg {
public:
    virtual void assertEvaluates(Value input, Value output) override {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionCeil(expCtx);
        ExpressionNaryTestOneArg::assertEvaluates(input, output);
    }
};

TEST_F(ExpressionCeilTest, IntArg) {
    assertEvaluates(Value(0), Value(0));
    assertEvaluates(Value(numeric_limits<int>::min()), Value(numeric_limits<int>::min()));
    assertEvaluates(Value(numeric_limits<int>::max()), Value(numeric_limits<int>::max()));
}

TEST_F(ExpressionCeilTest, LongArg) {
    assertEvaluates(Value(0LL), Value(0LL));
    assertEvaluates(Value(numeric_limits<long long>::min()),
                    Value(numeric_limits<long long>::min()));
    assertEvaluates(Value(numeric_limits<long long>::max()),
                    Value(numeric_limits<long long>::max()));
}

TEST_F(ExpressionCeilTest, DoubleArg) {
    assertEvaluates(Value(2.0), Value(2.0));
    assertEvaluates(Value(-2.0), Value(-2.0));
    assertEvaluates(Value(0.9), Value(1.0));
    assertEvaluates(Value(0.1), Value(1.0));
    assertEvaluates(Value(-1.2), Value(-1.0));
    assertEvaluates(Value(-1.7), Value(-1.0));

    // Outside the range of long longs (there isn't enough precision for decimals in this range, so
    // ceil should just preserve the number).
    double largerThanLong = numeric_limits<long long>::max() * 2.0;
    assertEvaluates(Value(largerThanLong), Value(largerThanLong));
    double smallerThanLong = numeric_limits<long long>::min() * 2.0;
    assertEvaluates(Value(smallerThanLong), Value(smallerThanLong));
}

TEST_F(ExpressionCeilTest, DecimalArg) {
    assertEvaluates(Value(Decimal128("2")), Value(Decimal128("2.0")));
    assertEvaluates(Value(Decimal128("-2")), Value(Decimal128("-2.0")));
    assertEvaluates(Value(Decimal128("0.9")), Value(Decimal128("1.0")));
    assertEvaluates(Value(Decimal128("0.1")), Value(Decimal128("1.0")));
    assertEvaluates(Value(Decimal128("-1.2")), Value(Decimal128("-1.0")));
    assertEvaluates(Value(Decimal128("-1.7")), Value(Decimal128("-1.0")));
    assertEvaluates(Value(Decimal128("1234567889.000000000000000000000001")),
                    Value(Decimal128("1234567890")));
    assertEvaluates(Value(Decimal128("-99999999999999999999999999999.99")),
                    Value(Decimal128("-99999999999999999999999999999.00")));
    assertEvaluates(Value(Decimal128("3.4E-6000")), Value(Decimal128("1")));
}

TEST_F(ExpressionCeilTest, NullArg) {
    assertEvaluates(Value(BSONNULL), Value(BSONNULL));
}

/* ------------------------- ExpressionFloor -------------------------- */

class ExpressionFloorTest : public ExpressionNaryTestOneArg {
public:
    virtual void assertEvaluates(Value input, Value output) override {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionFloor(expCtx);
        ExpressionNaryTestOneArg::assertEvaluates(input, output);
    }
};

TEST_F(ExpressionFloorTest, IntArg) {
    assertEvaluates(Value(0), Value(0));
    assertEvaluates(Value(numeric_limits<int>::min()), Value(numeric_limits<int>::min()));
    assertEvaluates(Value(numeric_limits<int>::max()), Value(numeric_limits<int>::max()));
}

TEST_F(ExpressionFloorTest, LongArg) {
    assertEvaluates(Value(0LL), Value(0LL));
    assertEvaluates(Value(numeric_limits<long long>::min()),
                    Value(numeric_limits<long long>::min()));
    assertEvaluates(Value(numeric_limits<long long>::max()),
                    Value(numeric_limits<long long>::max()));
}

TEST_F(ExpressionFloorTest, DoubleArg) {
    assertEvaluates(Value(2.0), Value(2.0));
    assertEvaluates(Value(-2.0), Value(-2.0));
    assertEvaluates(Value(0.9), Value(0.0));
    assertEvaluates(Value(0.1), Value(0.0));
    assertEvaluates(Value(-1.2), Value(-2.0));
    assertEvaluates(Value(-1.7), Value(-2.0));

    // Outside the range of long longs (there isn't enough precision for decimals in this range, so
    // floor should just preserve the number).
    double largerThanLong = numeric_limits<long long>::max() * 2.0;
    assertEvaluates(Value(largerThanLong), Value(largerThanLong));
    double smallerThanLong = numeric_limits<long long>::min() * 2.0;
    assertEvaluates(Value(smallerThanLong), Value(smallerThanLong));
}

TEST_F(ExpressionFloorTest, DecimalArg) {
    assertEvaluates(Value(Decimal128("2")), Value(Decimal128("2.0")));
    assertEvaluates(Value(Decimal128("-2")), Value(Decimal128("-2.0")));
    assertEvaluates(Value(Decimal128("0.9")), Value(Decimal128("0.0")));
    assertEvaluates(Value(Decimal128("0.1")), Value(Decimal128("0.0")));
    assertEvaluates(Value(Decimal128("-1.2")), Value(Decimal128("-2.0")));
    assertEvaluates(Value(Decimal128("-1.7")), Value(Decimal128("-2.0")));
    assertEvaluates(Value(Decimal128("1234567890.000000000000000000000001")),
                    Value(Decimal128("1234567890")));
    assertEvaluates(Value(Decimal128("-99999999999999999999999999999.99")),
                    Value(Decimal128("-100000000000000000000000000000")));
    assertEvaluates(Value(Decimal128("3.4E-6000")), Value(Decimal128("0")));
}

TEST_F(ExpressionFloorTest, NullArg) {
    assertEvaluates(Value(BSONNULL), Value(BSONNULL));
}

/* ------------------------ ExpressionRange --------------------------- */

TEST(ExpressionRangeTest, ComputesStandardRange) {
    assertExpectedResults("$range", {{{Value(0), Value(3)}, Value(BSON_ARRAY(0 << 1 << 2))}});
}

TEST(ExpressionRangeTest, ComputesRangeWithStep) {
    assertExpectedResults("$range",
                          {{{Value(0), Value(6), Value(2)}, Value(BSON_ARRAY(0 << 2 << 4))}});
}

TEST(ExpressionRangeTest, ComputesReverseRange) {
    assertExpectedResults("$range",
                          {{{Value(0), Value(-3), Value(-1)}, Value(BSON_ARRAY(0 << -1 << -2))}});
}

TEST(ExpressionRangeTest, ComputesRangeWithPositiveAndNegative) {
    assertExpectedResults("$range",
                          {{{Value(-2), Value(3)}, Value(BSON_ARRAY(-2 << -1 << 0 << 1 << 2))}});
}

TEST(ExpressionRangeTest, ComputesEmptyRange) {
    assertExpectedResults("$range",
                          {{{Value(-2), Value(3), Value(-1)}, Value(std::vector<Value>())}});
}

TEST(ExpressionRangeTest, ComputesRangeWithSameStartAndEnd) {
    assertExpectedResults("$range", {{{Value(20), Value(20)}, Value(std::vector<Value>())}});
}

TEST(ExpressionRangeTest, ComputesRangeWithLargeNegativeStep) {
    assertExpectedResults("$range",
                          {{{Value(3), Value(-5), Value(-3)}, Value(BSON_ARRAY(3 << 0 << -3))}});
}

/* ------------------------ ExpressionReverseArray -------------------- */

TEST(ExpressionReverseArrayTest, ReversesNormalArray) {
    assertExpectedResults("$reverseArray",
                          {{{Value(BSON_ARRAY(1 << 2 << 3))}, Value(BSON_ARRAY(3 << 2 << 1))}});
}

TEST(ExpressionReverseArrayTest, ReversesEmptyArray) {
    assertExpectedResults("$reverseArray",
                          {{{Value(std::vector<Value>())}, Value(std::vector<Value>())}});
}

TEST(ExpressionReverseArrayTest, ReversesOneElementArray) {
    assertExpectedResults("$reverseArray", {{{Value(BSON_ARRAY(1))}, Value(BSON_ARRAY(1))}});
}

TEST(ExpressionReverseArrayTest, ReturnsNullWithNullishInput) {
    assertExpectedResults(
        "$reverseArray",
        {{{Value(BSONNULL)}, Value(BSONNULL)}, {{Value(BSONUndefined)}, Value(BSONNULL)}});
}

/* ------------------------- ExpressionRound -------------------------- */

class ExpressionRoundOneArgTest : public ExpressionNaryTestOneArg {
public:
    void assertEval(ImplicitValue input, ImplicitValue output) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionRound(expCtx);
        ExpressionNaryTestOneArg::assertEvaluates(input, output);
    }
};

class ExpressionRoundTwoArgTest : public ExpressionNaryTestTwoArg {
public:
    void assertEval(ImplicitValue input1, ImplicitValue input2, ImplicitValue output) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionRound(expCtx);
        ExpressionNaryTestTwoArg::assertEvaluates(input1, input2, output);
    }
};

TEST_F(ExpressionRoundOneArgTest, IntArg1) {
    assertEval(0, 0);
    assertEval(numeric_limits<int>::min(), numeric_limits<int>::min());
    assertEval(numeric_limits<int>::max(), numeric_limits<int>::max());
}

TEST_F(ExpressionRoundTwoArgTest, IntArg2) {
    assertEval(0, 0, 0);
    assertEval(2, -1, 0);
    assertEval(29, -1, 30);
    assertEval(numeric_limits<int>::min(), 10, numeric_limits<int>::min());
    assertEval(numeric_limits<int>::max(), 42, numeric_limits<int>::max());
}

TEST_F(ExpressionRoundOneArgTest, LongArg1) {
    assertEval(0LL, 0LL);
    assertEval(numeric_limits<long long>::min(), numeric_limits<long long>::min());
    assertEval(numeric_limits<long long>::max(), numeric_limits<long long>::max());
}

TEST_F(ExpressionRoundTwoArgTest, LongArg2) {
    assertEval(0LL, 0LL, 0LL);
    assertEval(2LL, -1LL, 0LL);
    assertEval(29LL, -1LL, 30LL);
    assertEval(numeric_limits<long long>::min(), 10LL, numeric_limits<long long>::min());
    assertEval(numeric_limits<long long>::max(), 42LL, numeric_limits<long long>::max());
}

TEST_F(ExpressionRoundOneArgTest, DoubleArg1) {
    assertEval(2.0, 2.0);
    assertEval(-2.0, -2.0);
    assertEval(0.9, 1.0);
    assertEval(0.1, 0.0);
    assertEval(1.5, 2.0);
    assertEval(2.5, 2.0);
    assertEval(3.5, 4.0);
    assertEval(-1.2, -1.0);
    assertEval(-1.7, -2.0);
    assertEval(-1.5, -2.0);
    assertEval(-2.5, -2.0);

    // Outside the range of long longs (there isn't enough precision for decimals in this range, so
    // should just preserve the number).
    double largerThanLong = numeric_limits<long long>::max() * 2.0;
    assertEval(largerThanLong, largerThanLong);
    double smallerThanLong = numeric_limits<long long>::min() * 2.0;
    assertEval(smallerThanLong, smallerThanLong);
}

TEST_F(ExpressionRoundTwoArgTest, DoubleArg2) {
    assertEval(2.0, 1.0, 2.0);
    assertEval(-2.0, 2.0, -2.0);
    assertEval(0.9, 0, 1.0);
    assertEval(0.1, 0, 0.0);
    assertEval(1.5, 0, 2.0);
    assertEval(2.5, 0, 2.0);
    assertEval(3.5, 0, 4.0);
    assertEval(-1.2, 0, -1.0);
    assertEval(-1.7, 0, -2.0);
    assertEval(-1.5, 0, -2.0);
    assertEval(-2.5, 0, -2.0);

    assertEval(-3.14159265, 0, -3.0);
    assertEval(-3.14159265, 1, -3.1);
    assertEval(-3.14159265, 2, -3.14);
    assertEval(-3.14159265, 3, -3.142);
    assertEval(-3.14159265, 4, -3.1416);
    assertEval(-3.14159265, 5, -3.14159);
    assertEval(-3.14159265, 6, -3.141593);
    assertEval(-3.14159265, 7, -3.1415927);
    assertEval(-3.14159265, 100, -3.14159265);
    assertEval(3.14159265, 0, 3.0);
    assertEval(3.14159265, 1, 3.1);
    assertEval(3.14159265, 2, 3.14);
    assertEval(3.14159265, 3, 3.142);
    assertEval(3.14159265, 4, 3.1416);
    assertEval(3.14159265, 5, 3.14159);
    assertEval(3.14159265, 6, 3.141593);
    assertEval(3.14159265, 7, 3.1415927);
    assertEval(3.14159265, 100, 3.14159265);
    assertEval(3.14159265, -1, 0.0);
    assertEval(335.14159265, -1, 340.0);
    assertEval(333.14159265, -2, 300.0);
}

TEST_F(ExpressionRoundOneArgTest, DecimalArg1) {
    assertEval(Decimal128("2"), Decimal128("2.0"));
    assertEval(Decimal128("-2"), Decimal128("-2.0"));
    assertEval(Decimal128("0.9"), Decimal128("1.0"));
    assertEval(Decimal128("0.1"), Decimal128("0.0"));
    assertEval(Decimal128("0.5"), Decimal128("0.0"));
    assertEval(Decimal128("1.5"), Decimal128("2.0"));
    assertEval(Decimal128("2.5"), Decimal128("2.0"));
    assertEval(Decimal128("-1.2"), Decimal128("-1.0"));
    assertEval(Decimal128("-1.7"), Decimal128("-2.0"));
    assertEval(Decimal128("123456789.9999999999999999999999999"), Decimal128("123456790"));
    assertEval(Decimal128("-99999999999999999999999999999.99"),
               Decimal128("-100000000000000000000000000000"));
    assertEval(Decimal128("3.4E-6000"), Decimal128("0"));
}

TEST_F(ExpressionRoundTwoArgTest, DecimalArg2) {
    assertEval(Decimal128("2"), 0, Decimal128("2.0"));
    assertEval(Decimal128("-2"), 0, Decimal128("-2.0"));
    assertEval(Decimal128("0.9"), 0, Decimal128("1.0"));
    assertEval(Decimal128("0.1"), 0, Decimal128("0.0"));
    assertEval(Decimal128("0.5"), 0, Decimal128("0.0"));
    assertEval(Decimal128("1.5"), 0, Decimal128("2.0"));
    assertEval(Decimal128("2.5"), 0, Decimal128("2.0"));
    assertEval(Decimal128("-1.2"), 0, Decimal128("-1.0"));
    assertEval(Decimal128("-1.7"), 0, Decimal128("-2.0"));
    assertEval(Decimal128("123456789.9999999999999999999999999"), 0, Decimal128("123456790"));
    assertEval(Decimal128("-99999999999999999999999999999.99"),
               0,
               Decimal128("-100000000000000000000000000000"));
    assertEval(Decimal128("3.4E-6000"), 0, Decimal128("0"));

    assertEval(Decimal128("-3.14159265"), 0, Decimal128("-3.0"));
    assertEval(Decimal128("-3.14159265"), 1, Decimal128("-3.1"));
    assertEval(Decimal128("-3.14159265"), 2, Decimal128("-3.14"));
    assertEval(Decimal128("-3.14159265"), 3, Decimal128("-3.142"));
    assertEval(Decimal128("-3.14159265"), 4, Decimal128("-3.1416"));
    assertEval(Decimal128("-3.14159265"), 5, Decimal128("-3.14159"));
    assertEval(Decimal128("-3.14159265"), 6, Decimal128("-3.141593"));
    assertEval(Decimal128("-3.14159265"), 7, Decimal128("-3.1415926"));
    assertEval(Decimal128("-3.14159265"), 100, Decimal128("-3.14159265"));
    assertEval(Decimal128("3.14159265"), 0, Decimal128("3.0"));
    assertEval(Decimal128("3.14159265"), 1, Decimal128("3.1"));
    assertEval(Decimal128("3.14159265"), 2, Decimal128("3.14"));
    assertEval(Decimal128("3.14159265"), Decimal128("3"), Decimal128("3.142"));
    assertEval(Decimal128("3.14159265"), 4, Decimal128("3.1416"));
    assertEval(Decimal128("3.14159265"), Decimal128("5"), Decimal128("3.14159"));
    assertEval(Decimal128("3.14159265"), 6, Decimal128("3.141593"));
    assertEval(Decimal128("3.14159265"), 7, Decimal128("3.1415926"));
    assertEval(Decimal128("3.14159265"), 100, Decimal128("3.14159265"));
    assertEval(Decimal128("3.14159265"), Decimal128("-1"), Decimal128("0"));
    assertEval(Decimal128("335.14159265"), -1, Decimal128("340"));
    assertEval(Decimal128("333.14159265"), -2, Decimal128("300"));
}

TEST_F(ExpressionRoundOneArgTest, NullArg1) {
    assertEval(BSONNULL, BSONNULL);
}

TEST_F(ExpressionRoundTwoArgTest, NullArg2) {
    assertEval(BSONNULL, BSONNULL, BSONNULL);
    assertEval(1, BSONNULL, BSONNULL);
    assertEval(BSONNULL, 1, BSONNULL);
}

/* ------------------------- ExpressionTrunc -------------------------- */

class ExpressionTruncOneArgTest : public ExpressionNaryTestOneArg {
public:
    void assertEval(ImplicitValue input, ImplicitValue output) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionTrunc(expCtx);
        ExpressionNaryTestOneArg::assertEvaluates(input, output);
    }
};

class ExpressionTruncTwoArgTest : public ExpressionNaryTestTwoArg {
public:
    void assertEval(ImplicitValue input1, ImplicitValue input2, ImplicitValue output) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionTrunc(expCtx);
        ExpressionNaryTestTwoArg::assertEvaluates(input1, input2, output);
    }
};

TEST_F(ExpressionTruncOneArgTest, IntArg1) {
    assertEval(0, 0);
    assertEval(0, 0);
    assertEval(numeric_limits<int>::min(), numeric_limits<int>::min());
    assertEval(numeric_limits<int>::max(), numeric_limits<int>::max());
}

TEST_F(ExpressionTruncTwoArgTest, IntArg2) {
    assertEval(0, 0, 0);
    assertEval(2, -1, 0);
    assertEval(29, -1, 20);
    assertEval(numeric_limits<int>::min(), 10, numeric_limits<int>::min());
    assertEval(numeric_limits<int>::max(), 42, numeric_limits<int>::max());
}

TEST_F(ExpressionTruncOneArgTest, LongArg1) {
    assertEval(0LL, 0LL);
    assertEval(numeric_limits<long long>::min(), numeric_limits<long long>::min());
    assertEval(numeric_limits<long long>::max(), numeric_limits<long long>::max());
}

TEST_F(ExpressionTruncTwoArgTest, LongArg2) {
    assertEval(0LL, 0LL, 0LL);
    assertEval(2LL, -1LL, 0LL);
    assertEval(29LL, -1LL, 20LL);
    assertEval(numeric_limits<long long>::min(), 10LL, numeric_limits<long long>::min());
    assertEval(numeric_limits<long long>::max(), 42LL, numeric_limits<long long>::max());
}

TEST_F(ExpressionTruncOneArgTest, DoubleArg1) {
    assertEval(2.0, 2.0);
    assertEval(-2.0, -2.0);
    assertEval(0.9, 0.0);
    assertEval(0.1, 0.0);
    assertEval(0.5, 0.0);
    assertEval(1.5, 1.0);
    assertEval(2.5, 2.0);
    assertEval(-1.2, -1.0);
    assertEval(-1.7, -1.0);
    assertEval(-0.5, -0.0);
    assertEval(-1.5, -1.0);
    assertEval(-2.5, -2.0);

    // Outside the range of long longs (there isn't enough precision for decimals in this range, so
    // should just preserve the number).
    double largerThanLong = numeric_limits<long long>::max() * 2.0;
    assertEval(largerThanLong, largerThanLong);
    double smallerThanLong = numeric_limits<long long>::min() * 2.0;
    assertEval(smallerThanLong, smallerThanLong);
}

TEST_F(ExpressionTruncTwoArgTest, DoubleArg2) {
    assertEval(2.0, 1.0, 2.0);
    assertEval(-2.0, 2.0, -2.0);
    assertEval(0.9, 0, 0.0);
    assertEval(0.1, 0, 0.0);
    assertEval(0.5, 0, 0.0);
    assertEval(1.5, 0, 1.0);
    assertEval(2.5, 0, 2.0);
    assertEval(-1.2, 0, -1.0);
    assertEval(-1.7, 0, -1.0);
    assertEval(-0.5, 0, -0.0);
    assertEval(-1.5, 0, -1.0);
    assertEval(-2.5, 0, -2.0);

    assertEval(-3.14159265, 0, -3.0);
    assertEval(-3.14159265, 1, -3.1);
    assertEval(-3.14159265, 2, -3.14);
    assertEval(-3.14159265, 3, -3.141);
    assertEval(-3.14159265, 4, -3.1415);
    assertEval(-3.14159265, 5, -3.14159);
    assertEval(-3.14159265, 6, -3.141592);
    assertEval(-3.14159265, 7, -3.1415926);
    assertEval(-3.14159265, 100, -3.14159265);
    assertEval(3.14159265, 0, 3.0);
    assertEval(3.14159265, 1, 3.1);
    assertEval(3.14159265, 2, 3.14);
    assertEval(3.14159265, 3, 3.141);
    assertEval(3.14159265, 4, 3.1415);
    assertEval(3.14159265, 5, 3.14159);
    assertEval(3.14159265, 6, 3.141592);
    assertEval(3.14159265, 7, 3.1415926);
    assertEval(3.14159265, 100, 3.14159265);
    assertEval(3.14159265, -1, 0.0);
    assertEval(335.14159265, -1, 330.0);
    assertEval(333.14159265, -2, 300.0);
}

TEST_F(ExpressionTruncOneArgTest, DecimalArg1) {
    assertEval(Decimal128("2"), Decimal128("2.0"));
    assertEval(Decimal128("-2"), Decimal128("-2.0"));
    assertEval(Decimal128("0.9"), Decimal128("0.0"));
    assertEval(Decimal128("0.1"), Decimal128("0.0"));
    assertEval(Decimal128("-1.2"), Decimal128("-1.0"));
    assertEval(Decimal128("-1.7"), Decimal128("-1.0"));
    assertEval(Decimal128("123456789.9999999999999999999999999"), Decimal128("123456789"));
    assertEval(Decimal128("-99999999999999999999999999999.99"),
               Decimal128("-99999999999999999999999999999.00"));
    assertEval(Decimal128("3.4E-6000"), Decimal128("0"));
}

TEST_F(ExpressionTruncTwoArgTest, DecimalArg2) {
    assertEval(Decimal128("2"), 0, Decimal128("2.0"));
    assertEval(Decimal128("-2"), 0, Decimal128("-2.0"));
    assertEval(Decimal128("0.9"), 0, Decimal128("0.0"));
    assertEval(Decimal128("0.1"), 0, Decimal128("0.0"));
    assertEval(Decimal128("-1.2"), 0, Decimal128("-1.0"));
    assertEval(Decimal128("-1.7"), 0, Decimal128("-1.0"));
    assertEval(Decimal128("123456789.9999999999999999999999999"), 0, Decimal128("123456789"));
    assertEval(Decimal128("-99999999999999999999999999999.99"),
               0,
               Decimal128("-99999999999999999999999999999.00"));
    assertEval(Decimal128("3.4E-6000"), 0, Decimal128("0"));

    assertEval(Decimal128("-3.14159265"), 0, Decimal128("-3.0"));
    assertEval(Decimal128("-3.14159265"), 1, Decimal128("-3.1"));
    assertEval(Decimal128("-3.14159265"), 2, Decimal128("-3.14"));
    assertEval(Decimal128("-3.14159265"), 3, Decimal128("-3.141"));
    assertEval(Decimal128("-3.14159265"), 4, Decimal128("-3.1415"));
    assertEval(Decimal128("-3.14159265"), 5, Decimal128("-3.14159"));
    assertEval(Decimal128("-3.14159265"), 6, Decimal128("-3.141592"));
    assertEval(Decimal128("-3.14159265"), 7, Decimal128("-3.1415926"));
    assertEval(Decimal128("-3.14159265"), 100, Decimal128("-3.14159265"));
    assertEval(Decimal128("3.14159265"), 0, Decimal128("3.0"));
    assertEval(Decimal128("3.14159265"), 1, Decimal128("3.1"));
    assertEval(Decimal128("3.14159265"), 2, Decimal128("3.14"));
    assertEval(Decimal128("3.14159265"), Decimal128("3"), Decimal128("3.141"));
    assertEval(Decimal128("3.14159265"), 4, Decimal128("3.1415"));
    assertEval(Decimal128("3.14159265"), Decimal128("5"), Decimal128("3.14159"));
    assertEval(Decimal128("3.14159265"), 6, Decimal128("3.141592"));
    assertEval(Decimal128("3.14159265"), 7, Decimal128("3.1415926"));
    assertEval(Decimal128("3.14159265"), 100, Decimal128("3.14159265"));
    assertEval(Decimal128("3.14159265"), Decimal128("-1"), Decimal128("0"));
    assertEval(Decimal128("335.14159265"), -1, Decimal128("330"));
    assertEval(Decimal128("333.14159265"), -2, Decimal128("300"));
}

TEST_F(ExpressionTruncOneArgTest, NullArg1) {
    assertEval((BSONNULL), (BSONNULL));
}

TEST_F(ExpressionTruncTwoArgTest, NullArg2) {
    assertEval((BSONNULL), (BSONNULL), (BSONNULL));
    assertEval((1), (BSONNULL), (BSONNULL));
    assertEval((BSONNULL), (1), (BSONNULL));
}

/* ------------------------- ExpressionSqrt -------------------------- */

class ExpressionSqrtTest : public ExpressionNaryTestOneArg {
public:
    virtual void assertEvaluates(Value input, Value output) override {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionSqrt(expCtx);
        ExpressionNaryTestOneArg::assertEvaluates(input, output);
    }
};

TEST_F(ExpressionSqrtTest, SqrtIntArg) {
    assertEvaluates(Value(0), Value(0.0));
    assertEvaluates(Value(1), Value(1.0));
    assertEvaluates(Value(25), Value(5.0));
}

TEST_F(ExpressionSqrtTest, SqrtLongArg) {
    assertEvaluates(Value(0LL), Value(0.0));
    assertEvaluates(Value(1LL), Value(1.0));
    assertEvaluates(Value(25LL), Value(5.0));
    assertEvaluates(Value(40000000000LL), Value(200000.0));
}

TEST_F(ExpressionSqrtTest, SqrtDoubleArg) {
    assertEvaluates(Value(0.0), Value(0.0));
    assertEvaluates(Value(1.0), Value(1.0));
    assertEvaluates(Value(25.0), Value(5.0));
}

TEST_F(ExpressionSqrtTest, SqrtDecimalArg) {
    assertEvaluates(Value(Decimal128("0")), Value(Decimal128("0")));
    assertEvaluates(Value(Decimal128("1")), Value(Decimal128("1")));
    assertEvaluates(Value(Decimal128("25")), Value(Decimal128("5")));
    assertEvaluates(Value(Decimal128("30.25")), Value(Decimal128("5.5")));
}

TEST_F(ExpressionSqrtTest, SqrtNullArg) {
    assertEvaluates(Value(BSONNULL), Value(BSONNULL));
}

TEST_F(ExpressionSqrtTest, SqrtNaNArg) {
    assertEvaluates(Value(std::numeric_limits<double>::quiet_NaN()),
                    Value(std::numeric_limits<double>::quiet_NaN()));
}

/* ------------------------- ExpressionExp -------------------------- */

class ExpressionExpTest : public ExpressionNaryTestOneArg {
public:
    virtual void assertEvaluates(Value input, Value output) override {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        _expr = new ExpressionExp(expCtx);
        ExpressionNaryTestOneArg::assertEvaluates(input, output);
    }

    const Decimal128 decimalE = Decimal128("2.718281828459045235360287471352662");
};

TEST_F(ExpressionExpTest, ExpIntArg) {
    assertEvaluates(Value(0), Value(1.0));
    assertEvaluates(Value(1), Value(exp(1.0)));
}

TEST_F(ExpressionExpTest, ExpLongArg) {
    assertEvaluates(Value(0LL), Value(1.0));
    assertEvaluates(Value(1LL), Value(exp(1.0)));
}

TEST_F(ExpressionExpTest, ExpDoubleArg) {
    assertEvaluates(Value(0.0), Value(1.0));
    assertEvaluates(Value(1.0), Value(exp(1.0)));
}

TEST_F(ExpressionExpTest, ExpDecimalArg) {
    assertEvaluates(Value(Decimal128("0")), Value(Decimal128("1")));
    assertEvaluates(Value(Decimal128("1")), Value(decimalE));
}

TEST_F(ExpressionExpTest, ExpNullArg) {
    assertEvaluates(Value(BSONNULL), Value(BSONNULL));
}

TEST_F(ExpressionExpTest, ExpNaNArg) {
    assertEvaluates(Value(std::numeric_limits<double>::quiet_NaN()),
                    Value(std::numeric_limits<double>::quiet_NaN()));
}

/* ------------------------- Old-style tests -------------------------- */

namespace Add {

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<ExpressionNary> expression = new ExpressionAdd(expCtx);
        populateOperands(expression);
        ASSERT_BSONOBJ_EQ(expectedResult(), toBson(expression->evaluate(Document())));
    }

protected:
    virtual void populateOperands(intrusive_ptr<ExpressionNary>& expression) = 0;
    virtual BSONObj expectedResult() = 0;
};

/** $add with a NULL Document pointer, as called by ExpressionNary::optimize().
 */
class NullDocument {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<ExpressionNary> expression = new ExpressionAdd(expCtx);
        expression->addOperand(ExpressionConstant::create(expCtx, Value(2)));
        ASSERT_BSONOBJ_EQ(BSON("" << 2), toBson(expression->evaluate(Document())));
    }
};

/** $add without operands. */
class NoOperands : public ExpectedResultBase {
    void populateOperands(intrusive_ptr<ExpressionNary>& expression) {}
    virtual BSONObj expectedResult() {
        return BSON("" << 0);
    }
};

/** String type unsupported. */
class String {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<ExpressionNary> expression = new ExpressionAdd(expCtx);
        expression->addOperand(ExpressionConstant::create(expCtx, Value("a"_sd)));
        ASSERT_THROWS(expression->evaluate(Document()), AssertionException);
    }
};

/** Bool type unsupported. */
class Bool {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<ExpressionNary> expression = new ExpressionAdd(expCtx);
        expression->addOperand(ExpressionConstant::create(expCtx, Value(true)));
        ASSERT_THROWS(expression->evaluate(Document()), AssertionException);
    }
};

class SingleOperandBase : public ExpectedResultBase {
    void populateOperands(intrusive_ptr<ExpressionNary>& expression) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        expression->addOperand(ExpressionConstant::create(expCtx, valueFromBson(operand())));
    }
    BSONObj expectedResult() {
        return operand();
    }

protected:
    virtual BSONObj operand() = 0;
};

/** Single int argument. */
class Int : public SingleOperandBase {
    BSONObj operand() {
        return BSON("" << 1);
    }
};

/** Single long argument. */
class Long : public SingleOperandBase {
    BSONObj operand() {
        return BSON("" << 5555LL);
    }
};

/** Single double argument. */
class Double : public SingleOperandBase {
    BSONObj operand() {
        return BSON("" << 99.99);
    }
};

/** Single Date argument. */
class Date : public SingleOperandBase {
    BSONObj operand() {
        return BSON("" << Date_t::fromMillisSinceEpoch(12345));
    }
};

/** Single null argument. */
class Null : public SingleOperandBase {
    BSONObj operand() {
        return BSON("" << BSONNULL);
    }
    BSONObj expectedResult() {
        return BSON("" << BSONNULL);
    }
};

/** Single undefined argument. */
class Undefined : public SingleOperandBase {
    BSONObj operand() {
        return fromjson("{'':undefined}");
    }
    BSONObj expectedResult() {
        return BSON("" << BSONNULL);
    }
};

class TwoOperandBase : public ExpectedResultBase {
public:
    TwoOperandBase() : _reverse() {}
    void run() {
        ExpectedResultBase::run();
        // Now add the operands in the reverse direction.
        _reverse = true;
        ExpectedResultBase::run();
    }

protected:
    void populateOperands(intrusive_ptr<ExpressionNary>& expression) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        expression->addOperand(
            ExpressionConstant::create(expCtx, valueFromBson(_reverse ? operand2() : operand1())));
        expression->addOperand(
            ExpressionConstant::create(expCtx, valueFromBson(_reverse ? operand1() : operand2())));
    }
    virtual BSONObj operand1() = 0;
    virtual BSONObj operand2() = 0;

private:
    bool _reverse;
};

/** Add two ints. */
class IntInt : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << 1);
    }
    BSONObj operand2() {
        return BSON("" << 5);
    }
    BSONObj expectedResult() {
        return BSON("" << 6);
    }
};

/** Adding two large ints produces a long, not an overflowed int. */
class IntIntNoOverflow : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << numeric_limits<int>::max());
    }
    BSONObj operand2() {
        return BSON("" << numeric_limits<int>::max());
    }
    BSONObj expectedResult() {
        return BSON("" << ((long long)(numeric_limits<int>::max()) + numeric_limits<int>::max()));
    }
};

/** Adding an int and a long produces a long. */
class IntLong : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << 1);
    }
    BSONObj operand2() {
        return BSON("" << 9LL);
    }
    BSONObj expectedResult() {
        return BSON("" << 10LL);
    }
};

/** Adding an int and a long produces a double. */
class IntLongOverflowToDouble : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << numeric_limits<int>::max());
    }
    BSONObj operand2() {
        return BSON("" << numeric_limits<long long>::max());
    }
    BSONObj expectedResult() {
        // When the result cannot be represented in a NumberLong, a NumberDouble is returned.
        const auto im = numeric_limits<int>::max();
        const auto llm = numeric_limits<long long>::max();
        double result = static_cast<double>(im) + static_cast<double>(llm);
        return BSON("" << result);
    }
};

/** Adding an int and a double produces a double. */
class IntDouble : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << 9);
    }
    BSONObj operand2() {
        return BSON("" << 1.1);
    }
    BSONObj expectedResult() {
        return BSON("" << 10.1);
    }
};

/** Adding an int and a Date produces a Date. */
class IntDate : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << 6);
    }
    BSONObj operand2() {
        return BSON("" << Date_t::fromMillisSinceEpoch(123450));
    }
    BSONObj expectedResult() {
        return BSON("" << Date_t::fromMillisSinceEpoch(123456));
    }
};

/** Adding a long and a double produces a double. */
class LongDouble : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << 9LL);
    }
    BSONObj operand2() {
        return BSON("" << 1.1);
    }
    BSONObj expectedResult() {
        return BSON("" << 10.1);
    }
};

/** Adding a long and a double does not overflow. */
class LongDoubleNoOverflow : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << numeric_limits<long long>::max());
    }
    BSONObj operand2() {
        return BSON("" << double(numeric_limits<long long>::max()));
    }
    BSONObj expectedResult() {
        return BSON("" << numeric_limits<long long>::max() +
                        double(numeric_limits<long long>::max()));
    }
};

/** Adding an int and null. */
class IntNull : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << 1);
    }
    BSONObj operand2() {
        return BSON("" << BSONNULL);
    }
    BSONObj expectedResult() {
        return BSON("" << BSONNULL);
    }
};

/** Adding a long and undefined. */
class LongUndefined : public TwoOperandBase {
    BSONObj operand1() {
        return BSON("" << 5LL);
    }
    BSONObj operand2() {
        return fromjson("{'':undefined}");
    }
    BSONObj expectedResult() {
        return BSON("" << BSONNULL);
    }
};

}  // namespace Add

namespace And {

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObject = BSON("" << spec());
        BSONElement specElement = specObject.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult()),
                          toBson(expression->evaluate(fromBson(BSON("a" << 1)))));
        intrusive_ptr<Expression> optimized = expression->optimize();
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult()),
                          toBson(optimized->evaluate(fromBson(BSON("a" << 1)))));
    }

protected:
    virtual BSONObj spec() = 0;
    virtual bool expectedResult() = 0;
};

class OptimizeBase {
public:
    virtual ~OptimizeBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObject = BSON("" << spec());
        BSONElement specElement = specObject.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        intrusive_ptr<Expression> optimized = expression->optimize();
        ASSERT_BSONOBJ_EQ(expectedOptimized(), expressionToBson(optimized));
    }

protected:
    virtual BSONObj spec() = 0;
    virtual BSONObj expectedOptimized() = 0;
};

class NoOptimizeBase : public OptimizeBase {
    BSONObj expectedOptimized() {
        return constify(spec());
    }
};

/** $and without operands. */
class NoOperands : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSONArray());
    }
    bool expectedResult() {
        return true;
    }
};

/** $and passed 'true'. */
class True : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(true));
    }
    bool expectedResult() {
        return true;
    }
};

/** $and passed 'false'. */
class False : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $and passed 'true', 'true'. */
class TrueTrue : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(true << true));
    }
    bool expectedResult() {
        return true;
    }
};

/** $and passed 'true', 'false'. */
class TrueFalse : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(true << false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $and passed 'false', 'true'. */
class FalseTrue : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(false << true));
    }
    bool expectedResult() {
        return false;
    }
};

/** $and passed 'false', 'false'. */
class FalseFalse : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(false << false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $and passed 'true', 'true', 'true'. */
class TrueTrueTrue : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(true << true << true));
    }
    bool expectedResult() {
        return true;
    }
};

/** $and passed 'true', 'true', 'false'. */
class TrueTrueFalse : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(true << true << false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $and passed '0', '1'. */
class ZeroOne : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(0 << 1));
    }
    bool expectedResult() {
        return false;
    }
};

/** $and passed '1', '2'. */
class OneTwo : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(1 << 2));
    }
    bool expectedResult() {
        return true;
    }
};

/** $and passed a field path. */
class FieldPath : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
    bool expectedResult() {
        return true;
    }
};

/** A constant expression is optimized to a constant. */
class OptimizeConstantExpression : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(1));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

/** A non constant expression is not optimized. */
class NonConstant : public NoOptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
};

/** An expression beginning with a single constant is optimized. */
class ConstantNonConstantTrue : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(1 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
    // note: using $and as serialization of ExpressionCoerceToBool rather than
    // ExpressionAnd
};

class ConstantNonConstantFalse : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(0 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << false);
    }
};

/** An expression with a field path and '1'. */
class NonConstantOne : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY("$a" << 1));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
};

/** An expression with a field path and '0'. */
class NonConstantZero : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY("$a" << 0));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << false);
    }
};

/** An expression with two field paths and '1'. */
class NonConstantNonConstantOne : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY("$a"
                                         << "$b"
                                         << 1));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"
                                         << "$b"));
    }
};

/** An expression with two field paths and '0'. */
class NonConstantNonConstantZero : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY("$a"
                                         << "$b"
                                         << 0));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << false);
    }
};

/** An expression with '0', '1', and a field path. */
class ZeroOneNonConstant : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(0 << 1 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << false);
    }
};

/** An expression with '1', '1', and a field path. */
class OneOneNonConstant : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(1 << 1 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
};

/** Nested $and expressions. */
class Nested : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(1 << BSON("$and" << BSON_ARRAY(1)) << "$a"
                                           << "$b"));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"
                                         << "$b"));
    }
};

/** Nested $and expressions containing a nested value evaluating to false. */
class NestedZero : public OptimizeBase {
    BSONObj spec() {
        return BSON("$and" << BSON_ARRAY(
                        1 << BSON("$and" << BSON_ARRAY(BSON("$and" << BSON_ARRAY(0)))) << "$a"
                          << "$b"));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << false);
    }
};

}  // namespace And

namespace CoerceToBool {

/** Nested expression coerced to true. */
class EvaluateTrue {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> nested = ExpressionConstant::create(expCtx, Value(5));
        intrusive_ptr<Expression> expression = ExpressionCoerceToBool::create(expCtx, nested);
        ASSERT(expression->evaluate(Document()).getBool());
    }
};

/** Nested expression coerced to false. */
class EvaluateFalse {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> nested = ExpressionConstant::create(expCtx, Value(0));
        intrusive_ptr<Expression> expression = ExpressionCoerceToBool::create(expCtx, nested);
        ASSERT(!expression->evaluate(Document()).getBool());
    }
};

/** Dependencies forwarded from nested expression. */
class Dependencies {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> nested = ExpressionFieldPath::create(expCtx, "a.b");
        intrusive_ptr<Expression> expression = ExpressionCoerceToBool::create(expCtx, nested);
        DepsTracker dependencies;
        expression->addDependencies(&dependencies);
        ASSERT_EQUALS(1U, dependencies.fields.size());
        ASSERT_EQUALS(1U, dependencies.fields.count("a.b"));
        ASSERT_EQUALS(false, dependencies.needWholeDocument);
        ASSERT_EQUALS(false, dependencies.getNeedsMetadata(DepsTracker::MetadataType::TEXT_SCORE));
    }
};

/** Output to BSONObj. */
class AddToBsonObj {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression =
            ExpressionCoerceToBool::create(expCtx, ExpressionFieldPath::create(expCtx, "foo"));

        // serialized as $and because CoerceToBool isn't an ExpressionNary
        assertBinaryEqual(fromjson("{field:{$and:['$foo']}}"), toBsonObj(expression));
    }

private:
    static BSONObj toBsonObj(const intrusive_ptr<Expression>& expression) {
        return BSON("field" << expression->serialize(false));
    }
};

/** Output to BSONArray. */
class AddToBsonArray {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression =
            ExpressionCoerceToBool::create(expCtx, ExpressionFieldPath::create(expCtx, "foo"));

        // serialized as $and because CoerceToBool isn't an ExpressionNary
        assertBinaryEqual(BSON_ARRAY(fromjson("{$and:['$foo']}")), toBsonArray(expression));
    }

private:
    static BSONArray toBsonArray(const intrusive_ptr<Expression>& expression) {
        BSONArrayBuilder bab;
        bab << expression->serialize(false);
        return bab.arr();
    }
};

// TODO Test optimize(), difficult because a CoerceToBool cannot be output as
// BSON.

}  // namespace CoerceToBool

namespace Compare {

class OptimizeBase {
public:
    virtual ~OptimizeBase() {}
    void run() {
        BSONObj specObject = BSON("" << spec());
        BSONElement specElement = specObject.firstElement();
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        intrusive_ptr<Expression> optimized = expression->optimize();
        ASSERT_BSONOBJ_EQ(constify(expectedOptimized()), expressionToBson(optimized));
    }

protected:
    virtual BSONObj spec() = 0;
    virtual BSONObj expectedOptimized() = 0;
};

class FieldRangeOptimize : public OptimizeBase {
    BSONObj expectedOptimized() {
        return spec();
    }
};

class NoOptimize : public OptimizeBase {
    BSONObj expectedOptimized() {
        return spec();
    }
};

/** Check expected result for expressions depending on constants. */
class ExpectedResultBase : public OptimizeBase {
public:
    void run() {
        OptimizeBase::run();
        BSONObj specObject = BSON("" << spec());
        BSONElement specElement = specObject.firstElement();
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        // Check expression spec round trip.
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        // Check evaluation result.
        ASSERT_BSONOBJ_EQ(expectedResult(), toBson(expression->evaluate(Document())));
        // Check that the result is the same after optimizing.
        intrusive_ptr<Expression> optimized = expression->optimize();
        ASSERT_BSONOBJ_EQ(expectedResult(), toBson(optimized->evaluate(Document())));
    }

protected:
    virtual BSONObj spec() = 0;
    virtual BSONObj expectedResult() = 0;

private:
    virtual BSONObj expectedOptimized() {
        return BSON("$const" << expectedResult().firstElement());
    }
};

class ExpectedTrue : public ExpectedResultBase {
    BSONObj expectedResult() {
        return BSON("" << true);
    }
};

class ExpectedFalse : public ExpectedResultBase {
    BSONObj expectedResult() {
        return BSON("" << false);
    }
};

class ParseError {
public:
    virtual ~ParseError() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObject = BSON("" << spec());
        BSONElement specElement = specObject.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        ASSERT_THROWS(Expression::parseOperand(expCtx, specElement, vps), AssertionException);
    }

protected:
    virtual BSONObj spec() = 0;
};

/** $eq with first < second. */
class EqLt : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(1 << 2));
    }
};

/** $eq with first == second. */
class EqEq : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(1 << 1));
    }
};

/** $eq with first > second. */
class EqGt : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(1 << 0));
    }
};

/** $ne with first < second. */
class NeLt : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$ne" << BSON_ARRAY(1 << 2));
    }
};

/** $ne with first == second. */
class NeEq : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$ne" << BSON_ARRAY(1 << 1));
    }
};

/** $ne with first > second. */
class NeGt : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$ne" << BSON_ARRAY(1 << 0));
    }
};

/** $gt with first < second. */
class GtLt : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$gt" << BSON_ARRAY(1 << 2));
    }
};

/** $gt with first == second. */
class GtEq : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$gt" << BSON_ARRAY(1 << 1));
    }
};

/** $gt with first > second. */
class GtGt : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$gt" << BSON_ARRAY(1 << 0));
    }
};

/** $gte with first < second. */
class GteLt : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$gte" << BSON_ARRAY(1 << 2));
    }
};

/** $gte with first == second. */
class GteEq : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$gte" << BSON_ARRAY(1 << 1));
    }
};

/** $gte with first > second. */
class GteGt : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$gte" << BSON_ARRAY(1 << 0));
    }
};

/** $lt with first < second. */
class LtLt : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$lt" << BSON_ARRAY(1 << 2));
    }
};

/** $lt with first == second. */
class LtEq : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$lt" << BSON_ARRAY(1 << 1));
    }
};

/** $lt with first > second. */
class LtGt : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$lt" << BSON_ARRAY(1 << 0));
    }
};

/** $lte with first < second. */
class LteLt : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$lte" << BSON_ARRAY(1 << 2));
    }
};

/** $lte with first == second. */
class LteEq : public ExpectedTrue {
    BSONObj spec() {
        return BSON("$lte" << BSON_ARRAY(1 << 1));
    }
};

/** $lte with first > second. */
class LteGt : public ExpectedFalse {
    BSONObj spec() {
        return BSON("$lte" << BSON_ARRAY(1 << 0));
    }
};

/** $cmp with first < second. */
class CmpLt : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$cmp" << BSON_ARRAY(1 << 2));
    }
    BSONObj expectedResult() {
        return BSON("" << -1);
    }
};

/** $cmp with first == second. */
class CmpEq : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$cmp" << BSON_ARRAY(1 << 1));
    }
    BSONObj expectedResult() {
        return BSON("" << 0);
    }
};

/** $cmp with first > second. */
class CmpGt : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$cmp" << BSON_ARRAY(1 << 0));
    }
    BSONObj expectedResult() {
        return BSON("" << 1);
    }
};

/** $cmp results are bracketed to an absolute value of 1. */
class CmpBracketed : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$cmp" << BSON_ARRAY("z"
                                         << "a"));
    }
    BSONObj expectedResult() {
        return BSON("" << 1);
    }
};

/** Zero operands provided. */
class ZeroOperands : public ParseError {
    BSONObj spec() {
        return BSON("$ne" << BSONArray());
    }
};

/** One operand provided. */
class OneOperand : public ParseError {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(1));
    }
};

/** Three operands provided. */
class ThreeOperands : public ParseError {
    BSONObj spec() {
        return BSON("$gt" << BSON_ARRAY(2 << 3 << 4));
    }
};

/** Incompatible types can be compared. */
class IncompatibleTypes {
public:
    void run() {
        BSONObj specObject = BSON("" << BSON("$ne" << BSON_ARRAY("a" << 1)));
        BSONElement specElement = specObject.firstElement();
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_VALUE_EQ(expression->evaluate(Document()), Value(true));
    }
};

/**
 * An expression depending on constants is optimized to a constant via
 * ExpressionNary::optimize().
 */
class OptimizeConstants : public OptimizeBase {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(1 << 1));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

/** $cmp is not optimized. */
class NoOptimizeCmp : public NoOptimize {
    BSONObj spec() {
        return BSON("$cmp" << BSON_ARRAY(1 << "$a"));
    }
};

/** $ne is not optimized. */
class NoOptimizeNe : public NoOptimize {
    BSONObj spec() {
        return BSON("$ne" << BSON_ARRAY(1 << "$a"));
    }
};

/** No optimization is performend without a constant. */
class NoOptimizeNoConstant : public NoOptimize {
    BSONObj spec() {
        return BSON("$ne" << BSON_ARRAY("$a"
                                        << "$b"));
    }
};

/** No optimization is performend without an immediate field path. */
class NoOptimizeWithoutFieldPath : public NoOptimize {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(BSON("$and" << BSON_ARRAY("$a")) << 1));
    }
};

/** No optimization is performend without an immediate field path. */
class NoOptimizeWithoutFieldPathReverse : public NoOptimize {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(1 << BSON("$and" << BSON_ARRAY("$a"))));
    }
};

/** An equality expression is optimized. */
class OptimizeEq : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY("$a" << 1));
    }
};

/** A reverse sense equality expression is optimized. */
class OptimizeEqReverse : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$eq" << BSON_ARRAY(1 << "$a"));
    }
};

/** A $lt expression is optimized. */
class OptimizeLt : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$lt" << BSON_ARRAY("$a" << 1));
    }
};

/** A reverse sense $lt expression is optimized. */
class OptimizeLtReverse : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$lt" << BSON_ARRAY(1 << "$a"));
    }
};

/** A $lte expression is optimized. */
class OptimizeLte : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$lte" << BSON_ARRAY("$b" << 2));
    }
};

/** A reverse sense $lte expression is optimized. */
class OptimizeLteReverse : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$lte" << BSON_ARRAY(2 << "$b"));
    }
};

/** A $gt expression is optimized. */
class OptimizeGt : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$gt" << BSON_ARRAY("$b" << 2));
    }
};

/** A reverse sense $gt expression is optimized. */
class OptimizeGtReverse : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$gt" << BSON_ARRAY(2 << "$b"));
    }
};

/** A $gte expression is optimized. */
class OptimizeGte : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$gte" << BSON_ARRAY("$b" << 2));
    }
};

/** A reverse sense $gte expression is optimized. */
class OptimizeGteReverse : public FieldRangeOptimize {
    BSONObj spec() {
        return BSON("$gte" << BSON_ARRAY(2 << "$b"));
    }
};

}  // namespace Compare

namespace Constant {

/** Create an ExpressionConstant from a Value. */
class Create {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionConstant::create(expCtx, Value(5));
        assertBinaryEqual(BSON("" << 5), toBson(expression->evaluate(Document())));
    }
};

/** Create an ExpressionConstant from a BsonElement. */
class CreateFromBsonElement {
public:
    void run() {
        BSONObj spec = BSON("IGNORED_FIELD_NAME"
                            << "foo");
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONElement specElement = spec.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = ExpressionConstant::parse(expCtx, specElement, vps);
        assertBinaryEqual(BSON(""
                               << "foo"),
                          toBson(expression->evaluate(Document())));
    }
};

/** No optimization is performed. */
class Optimize {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionConstant::create(expCtx, Value(5));
        // An attempt to optimize returns the Expression itself.
        ASSERT_EQUALS(expression, expression->optimize());
    }
};

/** No dependencies. */
class Dependencies {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionConstant::create(expCtx, Value(5));
        DepsTracker dependencies;
        expression->addDependencies(&dependencies);
        ASSERT_EQUALS(0U, dependencies.fields.size());
        ASSERT_EQUALS(false, dependencies.needWholeDocument);
        ASSERT_EQUALS(false, dependencies.getNeedsMetadata(DepsTracker::MetadataType::TEXT_SCORE));
    }
};

/** Output to BSONObj. */
class AddToBsonObj {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionConstant::create(expCtx, Value(5));
        // The constant is replaced with a $ expression.
        assertBinaryEqual(BSON("field" << BSON("$const" << 5)), toBsonObj(expression));
    }

private:
    static BSONObj toBsonObj(const intrusive_ptr<Expression>& expression) {
        return BSON("field" << expression->serialize(false));
    }
};

/** Output to BSONArray. */
class AddToBsonArray {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionConstant::create(expCtx, Value(5));
        // The constant is copied out as is.
        assertBinaryEqual(constify(BSON_ARRAY(5)), toBsonArray(expression));
    }

private:
    static BSONObj toBsonArray(const intrusive_ptr<Expression>& expression) {
        BSONArrayBuilder bab;
        bab << expression->serialize(false);
        return bab.obj();
    }
};

TEST(ExpressionConstantTest, ConstantOfValueMissingRemovesField) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    intrusive_ptr<Expression> expression = ExpressionConstant::create(expCtx, Value());
    assertBinaryEqual(BSONObj(), toBson(expression->evaluate(Document{{"foo", Value("bar"_sd)}})));
}

TEST(ExpressionConstantTest, ConstantOfValueMissingSerializesToRemoveSystemVar) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    intrusive_ptr<Expression> expression = ExpressionConstant::create(expCtx, Value());
    assertBinaryEqual(BSON("field"
                           << "$$REMOVE"),
                      BSON("field" << expression->serialize(false)));
}

}  // namespace Constant

TEST(ExpressionFromAccumulators, Avg) {
    assertExpectedResults("$avg",
                          {// $avg ignores non-numeric inputs.
                           {{Value("string"_sd), Value(BSONNULL), Value(), Value(3)}, Value(3.0)},
                           // $avg always returns a double.
                           {{Value(10LL), Value(20LL)}, Value(15.0)},
                           // $avg returns null when no arguments are provided.
                           {{}, Value(BSONNULL)}});
}

TEST(ExpressionFromAccumulators, Max) {
    assertExpectedResults("$max",
                          {// $max treats non-numeric inputs as valid arguments.
                           {{Value(1), Value(BSONNULL), Value(), Value("a"_sd)}, Value("a"_sd)},
                           {{Value("a"_sd), Value("b"_sd)}, Value("b"_sd)},
                           // $max always preserves the type of the result.
                           {{Value(10LL), Value(0.0), Value(5)}, Value(10LL)},
                           // $max returns null when no arguments are provided.
                           {{}, Value(BSONNULL)}});
}

TEST(ExpressionFromAccumulators, Min) {
    assertExpectedResults("$min",
                          {// $min treats non-numeric inputs as valid arguments.
                           {{Value("string"_sd)}, Value("string"_sd)},
                           {{Value(1), Value(BSONNULL), Value(), Value("a"_sd)}, Value(1)},
                           {{Value("a"_sd), Value("b"_sd)}, Value("a"_sd)},
                           // $min always preserves the type of the result.
                           {{Value(0LL), Value(20.0), Value(10)}, Value(0LL)},
                           // $min returns null when no arguments are provided.
                           {{}, Value(BSONNULL)}});
}

TEST(ExpressionFromAccumulators, Sum) {
    assertExpectedResults(
        "$sum",
        {// $sum ignores non-numeric inputs.
         {{Value("string"_sd), Value(BSONNULL), Value(), Value(3)}, Value(3)},
         // If any argument is a double, $sum returns a double
         {{Value(10LL), Value(10.0)}, Value(20.0)},
         // If no arguments are doubles and an argument is a long, $sum returns a long
         {{Value(10LL), Value(10)}, Value(20LL)},
         // $sum returns 0 when no arguments are provided.
         {{}, Value(0)}});
}

TEST(ExpressionFromAccumulators, StdDevPop) {
    assertExpectedResults("$stdDevPop",
                          {// $stdDevPop ignores non-numeric inputs.
                           {{Value("string"_sd), Value(BSONNULL), Value(), Value(3)}, Value(0.0)},
                           // $stdDevPop always returns a double.
                           {{Value(1LL), Value(3LL)}, Value(1.0)},
                           // $stdDevPop returns null when no arguments are provided.
                           {{}, Value(BSONNULL)}});
}

TEST(ExpressionFromAccumulators, StdDevSamp) {
    assertExpectedResults(
        "$stdDevSamp",
        {// $stdDevSamp ignores non-numeric inputs.
         {{Value("string"_sd), Value(BSONNULL), Value(), Value(3)}, Value(BSONNULL)},
         // $stdDevSamp always returns a double.
         {{Value(1LL), Value(2LL), Value(3LL)}, Value(1.0)},
         // $stdDevSamp returns null when no arguments are provided.
         {{}, Value(BSONNULL)}});
}

TEST(ExpressionPowTest, LargeExponentValuesWithBaseOfZero) {
    assertExpectedResults(
        "$pow",
        {
            {{Value(0), Value(0)}, Value(1)},
            {{Value(0LL), Value(0LL)}, Value(1LL)},

            {{Value(0), Value(10)}, Value(0)},
            {{Value(0), Value(10000)}, Value(0)},

            {{Value(0LL), Value(10)}, Value(0LL)},

            // $pow may sometimes use a loop to compute a^b, so it's important to check
            // that the loop doesn't hang if a large exponent is provided.
            {{Value(0LL), Value(std::numeric_limits<long long>::max())}, Value(0LL)},
        });
}

TEST(ExpressionPowTest, ThrowsWhenBaseZeroAndExpNegative) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    const auto expr = Expression::parseExpression(expCtx, BSON("$pow" << BSON_ARRAY(0 << -5)), vps);
    ASSERT_THROWS([&] { expr->evaluate(Document()); }(), AssertionException);

    const auto exprWithLong =
        Expression::parseExpression(expCtx, BSON("$pow" << BSON_ARRAY(0LL << -5LL)), vps);
    ASSERT_THROWS([&] { expr->evaluate(Document()); }(), AssertionException);
}

TEST(ExpressionPowTest, LargeExponentValuesWithBaseOfOne) {
    assertExpectedResults(
        "$pow",
        {
            {{Value(1), Value(10)}, Value(1)},
            {{Value(1), Value(10LL)}, Value(1LL)},
            {{Value(1), Value(10000LL)}, Value(1LL)},

            {{Value(1LL), Value(10LL)}, Value(1LL)},

            // $pow may sometimes use a loop to compute a^b, so it's important to check
            // that the loop doesn't hang if a large exponent is provided.
            {{Value(1LL), Value(std::numeric_limits<long long>::max())}, Value(1LL)},
            {{Value(1LL), Value(std::numeric_limits<long long>::min())}, Value(1LL)},
        });
}

TEST(ExpressionPowTest, LargeExponentValuesWithBaseOfNegativeOne) {
    assertExpectedResults("$pow",
                          {
                              {{Value(-1), Value(-1)}, Value(-1)},
                              {{Value(-1), Value(-2)}, Value(1)},
                              {{Value(-1), Value(-3)}, Value(-1)},

                              {{Value(-1LL), Value(0LL)}, Value(1LL)},
                              {{Value(-1LL), Value(-1LL)}, Value(-1LL)},
                              {{Value(-1LL), Value(-2LL)}, Value(1LL)},
                              {{Value(-1LL), Value(-3LL)}, Value(-1LL)},
                              {{Value(-1LL), Value(-4LL)}, Value(1LL)},
                              {{Value(-1LL), Value(-5LL)}, Value(-1LL)},

                              {{Value(-1LL), Value(-61LL)}, Value(-1LL)},
                              {{Value(-1LL), Value(61LL)}, Value(-1LL)},

                              {{Value(-1LL), Value(-62LL)}, Value(1LL)},
                              {{Value(-1LL), Value(62LL)}, Value(1LL)},

                              {{Value(-1LL), Value(-101LL)}, Value(-1LL)},
                              {{Value(-1LL), Value(-102LL)}, Value(1LL)},

                              // Use a value large enough that will make the test hang for a
                              // considerable amount of time if a loop is used to compute the
                              // answer.
                              {{Value(-1LL), Value(63234673905128LL)}, Value(1LL)},
                              {{Value(-1LL), Value(-63234673905128LL)}, Value(1LL)},

                              {{Value(-1LL), Value(63234673905127LL)}, Value(-1LL)},
                              {{Value(-1LL), Value(-63234673905127LL)}, Value(-1LL)},
                          });
}

TEST(ExpressionPowTest, LargeBaseSmallPositiveExponent) {
    assertExpectedResults("$pow",
                          {
                              {{Value(4294967296LL), Value(1LL)}, Value(4294967296LL)},
                              {{Value(4294967296LL), Value(0)}, Value(1LL)},
                          });
}

TEST(ExpressionArray, ExpressionArrayWithAllConstantValuesShouldOptimizeToExpressionConstant) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    // ExpressionArray of constant values should optimize to ExpressionConsant.
    BSONObj bsonarrayOfConstants = BSON("" << BSON_ARRAY(1 << 2 << 3 << 4));
    BSONElement elementArray = bsonarrayOfConstants.firstElement();
    auto expressionArr = ExpressionArray::parse(expCtx, elementArray, vps);
    auto optimizedToConstant = expressionArr->optimize();
    auto exprConstant = dynamic_cast<ExpressionConstant*>(optimizedToConstant.get());
    ASSERT_TRUE(exprConstant);

    // ExpressionArray with not all constant values should not optimize to ExpressionConstant.
    BSONObj bsonarray = BSON("" << BSON_ARRAY(1 << "$x" << 3 << 4));
    BSONElement elementArrayNotConstant = bsonarray.firstElement();
    auto expressionArrNotConstant = ExpressionArray::parse(expCtx, elementArrayNotConstant, vps);
    auto notOptimized = expressionArrNotConstant->optimize();
    auto notExprConstant = dynamic_cast<ExpressionConstant*>(notOptimized.get());
    ASSERT_FALSE(notExprConstant);
}

TEST(ExpressionArray, ExpressionArrayShouldOptimizeSubExpressionToExpressionConstant) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;


    // ExpressionArray with constant values and sub expression that evaluates to constant should
    // optimize to Expression constant.
    BSONObj bsonarrayWithSubExpression =
        BSON("" << BSON_ARRAY(1 << BSON("$add" << BSON_ARRAY(1 << 1)) << 3 << 4));
    BSONElement elementArrayWithSubExpression = bsonarrayWithSubExpression.firstElement();
    auto expressionArrWithSubExpression =
        ExpressionArray::parse(expCtx, elementArrayWithSubExpression, vps);
    auto optimizedToConstantWithSubExpression = expressionArrWithSubExpression->optimize();
    auto constantExpression =
        dynamic_cast<ExpressionConstant*>(optimizedToConstantWithSubExpression.get());
    ASSERT_TRUE(constantExpression);
}

TEST(ExpressionIndexOfArray, ExpressionIndexOfArrayShouldOptimizeArguments) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    auto expIndexOfArray = Expression::parseExpression(
        expCtx,  // 2, 1, 1
        BSON("$indexOfArray" << BSON_ARRAY(
                 BSON_ARRAY(BSON("$add" << BSON_ARRAY(1 << 1)) << 1 << 1 << 2)
                 // Value we are searching for = 2.
                 << BSON("$add" << BSON_ARRAY(1 << 1))
                 // Start index = 1.
                 << BSON("$add" << BSON_ARRAY(0 << 1))
                 // End index = 4.
                 << BSON("$add" << BSON_ARRAY(1 << 3)))),
        expCtx->variablesParseState);
    auto argsOptimizedToConstants = expIndexOfArray->optimize();
    auto shouldBeIndexOfArray = dynamic_cast<ExpressionConstant*>(argsOptimizedToConstants.get());
    ASSERT_TRUE(shouldBeIndexOfArray);
    ASSERT_VALUE_EQ(Value(3), shouldBeIndexOfArray->getValue());
}

TEST(ExpressionIndexOfArray,
     ExpressionIndexOfArrayShouldOptimizeNullishInputArrayToExpressionConstant) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    auto expIndex = Expression::parseExpression(
        expCtx, fromjson("{ $indexOfArray : [ undefined , 1, 1]}"), expCtx->variablesParseState);

    auto isExpIndexOfArray = dynamic_cast<ExpressionIndexOfArray*>(expIndex.get());
    ASSERT_TRUE(isExpIndexOfArray);

    auto nullishValueOptimizedToExpConstant = isExpIndexOfArray->optimize();
    auto shouldBeExpressionConstant =
        dynamic_cast<ExpressionConstant*>(nullishValueOptimizedToExpConstant.get());
    ASSERT_TRUE(shouldBeExpressionConstant);
    // Nullish input array should become a Value(BSONNULL).
    ASSERT_VALUE_EQ(Value(BSONNULL), shouldBeExpressionConstant->getValue());
}

TEST(ExpressionIndexOfArray,
     OptimizedExpressionIndexOfArrayWithConstantArgumentsShouldEvaluateProperly) {

    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    auto expIndexOfArray = Expression::parseExpression(
        expCtx,
        // Search for $x.
        fromjson("{ $indexOfArray : [ [0, 1, 2, 3, 4, 5, 'val'] , '$x'] }"),
        expCtx->variablesParseState);
    auto optimizedIndexOfArray = expIndexOfArray->optimize();
    ASSERT_VALUE_EQ(Value(0), optimizedIndexOfArray->evaluate(Document{{"x", 0}}));
    ASSERT_VALUE_EQ(Value(1), optimizedIndexOfArray->evaluate(Document{{"x", 1}}));
    ASSERT_VALUE_EQ(Value(2), optimizedIndexOfArray->evaluate(Document{{"x", 2}}));
    ASSERT_VALUE_EQ(Value(3), optimizedIndexOfArray->evaluate(Document{{"x", 3}}));
    ASSERT_VALUE_EQ(Value(4), optimizedIndexOfArray->evaluate(Document{{"x", 4}}));
    ASSERT_VALUE_EQ(Value(5), optimizedIndexOfArray->evaluate(Document{{"x", 5}}));
    ASSERT_VALUE_EQ(Value(6), optimizedIndexOfArray->evaluate(Document{{"x", string("val")}}));

    auto optimizedIndexNotFound = optimizedIndexOfArray->optimize();
    // Should evaluate to -1 if not found.
    ASSERT_VALUE_EQ(Value(-1), optimizedIndexNotFound->evaluate(Document{{"x", 10}}));
    ASSERT_VALUE_EQ(Value(-1), optimizedIndexNotFound->evaluate(Document{{"x", 100}}));
    ASSERT_VALUE_EQ(Value(-1), optimizedIndexNotFound->evaluate(Document{{"x", 1000}}));
    ASSERT_VALUE_EQ(Value(-1), optimizedIndexNotFound->evaluate(Document{{"x", string("string")}}));
    ASSERT_VALUE_EQ(Value(-1), optimizedIndexNotFound->evaluate(Document{{"x", -1}}));
}

TEST(ExpressionIndexOfArray,
     OptimizedExpressionIndexOfArrayWithConstantArgumentsShouldEvaluateProperlyWithRange) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    auto expIndexOfArray = Expression::parseExpression(
        expCtx,
        // Search for 4 between 3 and 5.
        fromjson("{ $indexOfArray : [ [0, 1, 2, 3, 4, 5] , '$x', 3, 5] }"),
        expCtx->variablesParseState);
    auto optimizedIndexOfArray = expIndexOfArray->optimize();
    ASSERT_VALUE_EQ(Value(4), optimizedIndexOfArray->evaluate(Document{{"x", 4}}));

    // Should evaluate to -1 if not found in range.
    ASSERT_VALUE_EQ(Value(-1), optimizedIndexOfArray->evaluate(Document{{"x", 0}}));
}

TEST(ExpressionIndexOfArray,
     OptimizedExpressionIndexOfArrayWithConstantArrayShouldEvaluateProperlyWithDuplicateValues) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    auto expIndexOfArrayWithDuplicateValues =
        Expression::parseExpression(expCtx,
                                    // Search for 4 between 3 and 5.
                                    fromjson("{ $indexOfArray : [ [0, 1, 2, 2, 3, 4, 5] , '$x'] }"),
                                    expCtx->variablesParseState);
    auto optimizedIndexOfArrayWithDuplicateValues = expIndexOfArrayWithDuplicateValues->optimize();
    ASSERT_VALUE_EQ(Value(2),
                    optimizedIndexOfArrayWithDuplicateValues->evaluate(Document{{"x", 2}}));
    // Duplicate Values in a range.
    auto expIndexInRangeWithhDuplicateValues = Expression::parseExpression(
        expCtx,
        // Search for 2 between 4 and 6.
        fromjson("{ $indexOfArray : [ [0, 1, 2, 2, 2, 2, 4, 5] , '$x', 4, 6] }"),
        expCtx->variablesParseState);
    auto optimizedIndexInRangeWithDuplcateValues = expIndexInRangeWithhDuplicateValues->optimize();
    // Should evaluate to 4.
    ASSERT_VALUE_EQ(Value(4),
                    optimizedIndexInRangeWithDuplcateValues->evaluate(Document{{"x", 2}}));
}

namespace FieldPath {

/** The provided field path does not pass validation. */
class Invalid {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        ASSERT_THROWS(ExpressionFieldPath::create(expCtx, ""), AssertionException);
    }
};

TEST(FieldPath, NoOptimizationForRootFieldPathWithDottedPath) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    intrusive_ptr<ExpressionFieldPath> expression =
        ExpressionFieldPath::parse(expCtx, "$$ROOT.x.y", expCtx->variablesParseState);

    // An attempt to optimize returns the Expression itself.
    ASSERT_EQUALS(expression, expression->optimize());
}

TEST(FieldPath, NoOptimizationForCurrentFieldPathWithDottedPath) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    intrusive_ptr<ExpressionFieldPath> expression =
        ExpressionFieldPath::parse(expCtx, "$$CURRENT.x.y", expCtx->variablesParseState);

    // An attempt to optimize returns the Expression itself.
    ASSERT_EQUALS(expression, expression->optimize());
}

TEST(FieldPath, RemoveOptimizesToMissingValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    intrusive_ptr<ExpressionFieldPath> expression =
        ExpressionFieldPath::parse(expCtx, "$$REMOVE", expCtx->variablesParseState);

    auto optimizedExpr = expression->optimize();

    ASSERT_VALUE_EQ(Value(), optimizedExpr->evaluate(Document(BSON("x" << BSON("y" << 123)))));
}

TEST(FieldPath, NoOptimizationOnNormalPath) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a");
    // An attempt to optimize returns the Expression itself.
    ASSERT_EQUALS(expression, expression->optimize());
}

TEST(FieldPath, OptimizeOnVariableWithConstantScalarValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varId = expCtx->variablesParseState.defineVariable("userVar");
    expCtx->variables.setConstantValue(varId, Value(123));

    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar", expCtx->variablesParseState);
    ASSERT_TRUE(dynamic_cast<ExpressionFieldPath*>(expr.get()));

    auto optimizedExpr = expr->optimize();
    ASSERT_TRUE(dynamic_cast<ExpressionConstant*>(optimizedExpr.get()));
}

TEST(FieldPath, OptimizeOnVariableWithConstantArrayValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varId = expCtx->variablesParseState.defineVariable("userVar");
    expCtx->variables.setConstantValue(varId, Value(BSON_ARRAY(1 << 2 << 3)));

    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar", expCtx->variablesParseState);
    ASSERT_TRUE(dynamic_cast<ExpressionFieldPath*>(expr.get()));

    auto optimizedExpr = expr->optimize();
    auto constantExpr = dynamic_cast<ExpressionConstant*>(optimizedExpr.get());
    ASSERT_TRUE(constantExpr);
    ASSERT_VALUE_EQ(Value(BSON_ARRAY(1 << 2 << 3)), constantExpr->getValue());
}

TEST(FieldPath, OptimizeToEmptyArrayOnNumericalPathComponentAndConstantArrayValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varId = expCtx->variablesParseState.defineVariable("userVar");
    expCtx->variables.setConstantValue(varId, Value(BSON_ARRAY(1 << 2 << 3)));

    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar.1", expCtx->variablesParseState);
    ASSERT_TRUE(dynamic_cast<ExpressionFieldPath*>(expr.get()));

    auto optimizedExpr = expr->optimize();
    auto constantExpr = dynamic_cast<ExpressionConstant*>(optimizedExpr.get());
    ASSERT_TRUE(constantExpr);
    ASSERT_VALUE_EQ(Value(BSONArray()), constantExpr->getValue());
}

TEST(FieldPath, OptimizeOnVariableWithConstantValueAndDottedPath) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varId = expCtx->variablesParseState.defineVariable("userVar");
    expCtx->variables.setConstantValue(varId, Value(Document{{"x", Document{{"y", 123}}}}));

    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar.x.y", expCtx->variablesParseState);
    ASSERT_TRUE(dynamic_cast<ExpressionFieldPath*>(expr.get()));

    auto optimizedExpr = expr->optimize();
    auto constantExpr = dynamic_cast<ExpressionConstant*>(optimizedExpr.get());
    ASSERT_TRUE(constantExpr);
    ASSERT_VALUE_EQ(Value(123), constantExpr->getValue());
}

TEST(FieldPath, NoOptimizationOnVariableWithNoValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    expCtx->variablesParseState.defineVariable("userVar");

    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar", expCtx->variablesParseState);
    ASSERT_TRUE(dynamic_cast<ExpressionFieldPath*>(expr.get()));

    auto optimizedExpr = expr->optimize();
    ASSERT_FALSE(dynamic_cast<ExpressionConstant*>(optimizedExpr.get()));
}

TEST(FieldPath, NoOptimizationOnVariableWithMissingValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varId = expCtx->variablesParseState.defineVariable("userVar");
    expCtx->variables.setValue(varId, Value());

    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar", expCtx->variablesParseState);
    ASSERT_TRUE(dynamic_cast<ExpressionFieldPath*>(expr.get()));

    auto optimizedExpr = expr->optimize();
    ASSERT_FALSE(dynamic_cast<ExpressionConstant*>(optimizedExpr.get()));
}

TEST(FieldPath, ScalarVariableWithDottedFieldPathOptimizesToConstantMissingValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varId = expCtx->variablesParseState.defineVariable("userVar");
    expCtx->variables.setConstantValue(varId, Value(123));

    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar.x.y", expCtx->variablesParseState);
    ASSERT_TRUE(dynamic_cast<ExpressionFieldPath*>(expr.get()));

    auto optimizedExpr = expr->optimize();
    auto constantExpr = dynamic_cast<ExpressionConstant*>(optimizedExpr.get());
    ASSERT_TRUE(constantExpr);
    ASSERT_VALUE_EQ(Value(), constantExpr->getValue());
}

/** The field path itself is a dependency. */
class Dependencies {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        DepsTracker dependencies;
        expression->addDependencies(&dependencies);
        ASSERT_EQUALS(1U, dependencies.fields.size());
        ASSERT_EQUALS(1U, dependencies.fields.count("a.b"));
        ASSERT_EQUALS(false, dependencies.needWholeDocument);
        ASSERT_EQUALS(false, dependencies.getNeedsMetadata(DepsTracker::MetadataType::TEXT_SCORE));
    }
};

/** Field path target field is missing. */
class Missing {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a");
        assertBinaryEqual(fromjson("{}"), toBson(expression->evaluate(Document())));
    }
};

/** Simple case where the target field is present. */
class Present {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a");
        assertBinaryEqual(fromjson("{'':123}"),
                          toBson(expression->evaluate(fromBson(BSON("a" << 123)))));
    }
};

/** Target field parent is null. */
class NestedBelowNull {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{}"),
                          toBson(expression->evaluate(fromBson(fromjson("{a:null}")))));
    }
};

/** Target field parent is undefined. */
class NestedBelowUndefined {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{}"),
                          toBson(expression->evaluate(fromBson(fromjson("{a:undefined}")))));
    }
};

/** Target field parent is missing. */
class NestedBelowMissing {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{}"),
                          toBson(expression->evaluate(fromBson(fromjson("{z:1}")))));
    }
};

/** Target field parent is an integer. */
class NestedBelowInt {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{}"), toBson(expression->evaluate(fromBson(BSON("a" << 2)))));
    }
};

/** A value in a nested object. */
class NestedValue {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(BSON("" << 55),
                          toBson(expression->evaluate(fromBson(BSON("a" << BSON("b" << 55))))));
    }
};

/** Target field within an empty object. */
class NestedBelowEmptyObject {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{}"),
                          toBson(expression->evaluate(fromBson(BSON("a" << BSONObj())))));
    }
};

/** Target field within an empty array. */
class NestedBelowEmptyArray {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(BSON("" << BSONArray()),
                          toBson(expression->evaluate(fromBson(BSON("a" << BSONArray())))));
    }
};

/** Target field within an array containing null. */
class NestedBelowArrayWithNull {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{'':[]}"),
                          toBson(expression->evaluate(fromBson(fromjson("{a:[null]}")))));
    }
};

/** Target field within an array containing undefined. */
class NestedBelowArrayWithUndefined {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{'':[]}"),
                          toBson(expression->evaluate(fromBson(fromjson("{a:[undefined]}")))));
    }
};

/** Target field within an array containing an integer. */
class NestedBelowArrayWithInt {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{'':[]}"),
                          toBson(expression->evaluate(fromBson(fromjson("{a:[1]}")))));
    }
};

/** Target field within an array. */
class NestedWithinArray {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{'':[9]}"),
                          toBson(expression->evaluate(fromBson(fromjson("{a:[{b:9}]}")))));
    }
};

/** Multiple value types within an array. */
class MultipleArrayValues {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b");
        assertBinaryEqual(fromjson("{'':[9,20]}"),
                          toBson(expression->evaluate(
                              fromBson(fromjson("{a:[{b:9},null,undefined,{g:4},{b:20},{}]}")))));
    }
};

/** Expanding values within nested arrays. */
class ExpandNestedArrays {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b.c");
        assertBinaryEqual(fromjson("{'':[[1,2],3,[4],[[5]],[6,7]]}"),
                          toBson(expression->evaluate(fromBson(fromjson("{a:[{b:[{c:1},{c:2}]},"
                                                                        "{b:{c:3}},"
                                                                        "{b:[{c:4}]},"
                                                                        "{b:[{c:[5]}]},"
                                                                        "{b:{c:[6,7]}}]}")))));
    }
};

/** Add to a BSONObj. */
class AddToBsonObj {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b.c");
        assertBinaryEqual(BSON("foo"
                               << "$a.b.c"),
                          BSON("foo" << expression->serialize(false)));
    }
};

/** Add to a BSONArray. */
class AddToBsonArray {
public:
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        intrusive_ptr<Expression> expression = ExpressionFieldPath::create(expCtx, "a.b.c");
        BSONArrayBuilder bab;
        bab << expression->serialize(false);
        assertBinaryEqual(BSON_ARRAY("$a.b.c"), bab.arr());
    }
};

}  // namespace FieldPath

namespace Object {
using mongo::ExpressionObject;

template <typename T>
Document literal(T&& value) {
    return Document{{"$const", Value(std::forward<T>(value))}};
}

//
// Parsing.
//

TEST(ExpressionObjectParse, ShouldAcceptEmptyObject) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto object = ExpressionObject::parse(expCtx, BSONObj(), vps);
    ASSERT_VALUE_EQ(Value(Document{}), object->serialize(false));
}

TEST(ExpressionObjectParse, ShouldAcceptLiteralsAsValues) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto object = ExpressionObject::parse(expCtx,
                                          BSON("a" << 5 << "b"
                                                   << "string"
                                                   << "c"
                                                   << BSONNULL),
                                          vps);
    auto expectedResult =
        Value(Document{{"a", literal(5)}, {"b", literal("string"_sd)}, {"c", literal(BSONNULL)}});
    ASSERT_VALUE_EQ(expectedResult, object->serialize(false));
}

TEST(ExpressionObjectParse, ShouldAccept_idAsFieldName) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto object = ExpressionObject::parse(expCtx, BSON("_id" << 5), vps);
    auto expectedResult = Value(Document{{"_id", literal(5)}});
    ASSERT_VALUE_EQ(expectedResult, object->serialize(false));
}

TEST(ExpressionObjectParse, ShouldAcceptFieldNameContainingDollar) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto object = ExpressionObject::parse(expCtx, BSON("a$b" << 5), vps);
    auto expectedResult = Value(Document{{"a$b", literal(5)}});
    ASSERT_VALUE_EQ(expectedResult, object->serialize(false));
}

TEST(ExpressionObjectParse, ShouldAcceptNestedObjects) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto object =
        ExpressionObject::parse(expCtx, fromjson("{a: {b: 1}, c: {d: {e: 1, f: 1}}}"), vps);
    auto expectedResult =
        Value(Document{{"a", Document{{"b", literal(1)}}},
                       {"c", Document{{"d", Document{{"e", literal(1)}, {"f", literal(1)}}}}}});
    ASSERT_VALUE_EQ(expectedResult, object->serialize(false));
}

TEST(ExpressionObjectParse, ShouldAcceptArrays) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto object = ExpressionObject::parse(expCtx, fromjson("{a: [1, 2]}"), vps);
    auto expectedResult =
        Value(Document{{"a", vector<Value>{Value(literal(1)), Value(literal(2))}}});
    ASSERT_VALUE_EQ(expectedResult, object->serialize(false));
}

TEST(ObjectParsing, ShouldAcceptExpressionAsValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto object = ExpressionObject::parse(expCtx, BSON("a" << BSON("$and" << BSONArray())), vps);
    ASSERT_VALUE_EQ(object->serialize(false),
                    Value(Document{{"a", Document{{"$and", BSONArray()}}}}));
}

//
// Error cases.
//

TEST(ExpressionObjectParse, ShouldRejectDottedFieldNames) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON("a.b" << 1), vps), AssertionException);
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON("c" << 3 << "a.b" << 1), vps),
                  AssertionException);
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON("a.b" << 1 << "c" << 3), vps),
                  AssertionException);
}

TEST(ExpressionObjectParse, ShouldRejectDuplicateFieldNames) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON("a" << 1 << "a" << 1), vps),
                  AssertionException);
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON("a" << 1 << "b" << 2 << "a" << 1), vps),
                  AssertionException);
    ASSERT_THROWS(
        ExpressionObject::parse(expCtx, BSON("a" << BSON("c" << 1) << "b" << 2 << "a" << 1), vps),
        AssertionException);
    ASSERT_THROWS(
        ExpressionObject::parse(expCtx, BSON("a" << 1 << "b" << 2 << "a" << BSON("c" << 1)), vps),
        AssertionException);
}

TEST(ExpressionObjectParse, ShouldRejectInvalidFieldName) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON("$a" << 1), vps), AssertionException);
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON("" << 1), vps), AssertionException);
    ASSERT_THROWS(ExpressionObject::parse(expCtx, BSON(std::string("a\0b", 3) << 1), vps),
                  AssertionException);
}

TEST(ExpressionObjectParse, ShouldRejectInvalidFieldPathAsValue) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    ASSERT_THROWS(ExpressionObject::parse(expCtx,
                                          BSON("a"
                                               << "$field."),
                                          vps),
                  AssertionException);
}

TEST(ParseObject, ShouldRejectExpressionAsTheSecondField) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    ASSERT_THROWS(
        ExpressionObject::parse(
            expCtx, BSON("a" << BSON("$and" << BSONArray()) << "$or" << BSONArray()), vps),
        AssertionException);
}

//
// Evaluation.
//

namespace {
/**
 * ExpressionObject builds two vectors within it's ::parse() method, one owning and one with names
 * and references to the former. Since the ::create() method bypasses this step, we have to mimic
 * the behavior here.
 */
auto expressionObjectCreateHelper(
    const boost::intrusive_ptr<ExpressionContext>& expCtx,
    std::vector<std::pair<std::string, boost::intrusive_ptr<Expression>>>&&
        expressionsWithChildrenInPlace) {
    std::vector<boost::intrusive_ptr<Expression>> children;
    std::vector<std::pair<std::string, boost::intrusive_ptr<Expression>&>> expressions;
    for (auto & [ unused, expression ] : expressionsWithChildrenInPlace)
        children.push_back(std::move(expression));
    std::vector<boost::intrusive_ptr<Expression>>::size_type index = 0;
    for (auto & [ fieldName, unused ] : expressionsWithChildrenInPlace) {
        expressions.emplace_back(fieldName, children[index]);
        ++index;
    }
    return ExpressionObject::create(expCtx, std::move(children), std::move(expressions));
}
}  // namespace

TEST(ExpressionObjectEvaluate, EmptyObjectShouldEvaluateToEmptyDocument) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object = expressionObjectCreateHelper(expCtx, {});
    ASSERT_VALUE_EQ(Value(Document()), object->evaluate(Document()));
    ASSERT_VALUE_EQ(Value(Document()), object->evaluate(Document{{"a", 1}}));
    ASSERT_VALUE_EQ(Value(Document()), object->evaluate(Document{{"_id", "ID"_sd}}));
}

TEST(ExpressionObjectEvaluate, ShouldEvaluateEachField) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object =
        expressionObjectCreateHelper(expCtx, {{"a", makeConstant(1)}, {"b", makeConstant(5)}});
    ASSERT_VALUE_EQ(Value(Document{{"a", 1}, {"b", 5}}), object->evaluate(Document()));
    ASSERT_VALUE_EQ(Value(Document{{"a", 1}, {"b", 5}}), object->evaluate(Document{{"a", 1}}));
    ASSERT_VALUE_EQ(Value(Document{{"a", 1}, {"b", 5}}),
                    object->evaluate(Document{{"_id", "ID"_sd}}));
}

TEST(ExpressionObjectEvaluate, OrderOfFieldsInOutputShouldMatchOrderInSpecification) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object = expressionObjectCreateHelper(expCtx,
                                               {{"a", ExpressionFieldPath::create(expCtx, "a")},
                                                {"b", ExpressionFieldPath::create(expCtx, "b")},
                                                {"c", ExpressionFieldPath::create(expCtx, "c")}});
    ASSERT_VALUE_EQ(
        Value(Document{{"a", "A"_sd}, {"b", "B"_sd}, {"c", "C"_sd}}),
        object->evaluate(Document{{"c", "C"_sd}, {"a", "A"_sd}, {"b", "B"_sd}, {"_id", "ID"_sd}}));
}

TEST(ExpressionObjectEvaluate, ShouldRemoveFieldsThatHaveMissingValues) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object =
        expressionObjectCreateHelper(expCtx,
                                     {{"a", ExpressionFieldPath::create(expCtx, "a.b")},
                                      {"b", ExpressionFieldPath::create(expCtx, "missing")}});
    ASSERT_VALUE_EQ(Value(Document{}), object->evaluate(Document()));
    ASSERT_VALUE_EQ(Value(Document{}), object->evaluate(Document{{"a", 1}}));
}

TEST(ExpressionObjectEvaluate, ShouldEvaluateFieldsWithinNestedObject) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object = expressionObjectCreateHelper(
        expCtx,
        {{"a",
          expressionObjectCreateHelper(
              expCtx,
              {{"b", makeConstant(1)}, {"c", ExpressionFieldPath::create(expCtx, "_id")}})}});
    ASSERT_VALUE_EQ(Value(Document{{"a", Document{{"b", 1}}}}), object->evaluate(Document()));
    ASSERT_VALUE_EQ(Value(Document{{"a", Document{{"b", 1}, {"c", "ID"_sd}}}}),
                    object->evaluate(Document{{"_id", "ID"_sd}}));
}

TEST(ExpressionObjectEvaluate, ShouldEvaluateToEmptyDocumentIfAllFieldsAreMissing) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object = expressionObjectCreateHelper(
        expCtx, {{"a", ExpressionFieldPath::create(expCtx, "missing")}});
    ASSERT_VALUE_EQ(Value(Document{}), object->evaluate(Document()));

    auto objectWithNestedObject = expressionObjectCreateHelper(expCtx, {{"nested", object}});
    ASSERT_VALUE_EQ(Value(Document{{"nested", Document{}}}),
                    objectWithNestedObject->evaluate(Document()));
}

//
// Dependencies.
//

TEST(ExpressionObjectDependencies, ConstantValuesShouldNotBeAddedToDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object = expressionObjectCreateHelper(expCtx, {{"a", makeConstant(5)}});
    DepsTracker deps;
    object->addDependencies(&deps);
    ASSERT_EQ(deps.fields.size(), 0UL);
}

TEST(ExpressionObjectDependencies, FieldPathsShouldBeAddedToDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto object =
        expressionObjectCreateHelper(expCtx, {{"x", ExpressionFieldPath::create(expCtx, "c.d")}});
    DepsTracker deps;
    object->addDependencies(&deps);
    ASSERT_EQ(deps.fields.size(), 1UL);
    ASSERT_EQ(deps.fields.count("c.d"), 1UL);
};

TEST(ExpressionObjectDependencies, VariablesShouldBeAddedToDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varID = expCtx->variablesParseState.defineVariable("var1");
    auto fieldPath = ExpressionFieldPath::parse(expCtx, "$$var1", expCtx->variablesParseState);
    DepsTracker deps;
    fieldPath->addDependencies(&deps);
    ASSERT_EQ(deps.vars.size(), 1UL);
    ASSERT_EQ(deps.vars.count(varID), 1UL);
}

TEST(ExpressionObjectDependencies, LocalLetVariablesShouldBeFilteredOutOfDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    expCtx->variablesParseState.defineVariable("var1");
    auto letSpec = BSON("$let" << BSON("vars" << BSON("var2"
                                                      << "abc")
                                              << "in"
                                              << BSON("$multiply" << BSON_ARRAY("$$var1"
                                                                                << "$$var2"))));
    auto expressionLet =
        ExpressionLet::parse(expCtx, letSpec.firstElement(), expCtx->variablesParseState);
    DepsTracker deps;
    expressionLet->addDependencies(&deps);
    ASSERT_EQ(deps.vars.size(), 1UL);
    ASSERT_EQ(expCtx->variablesParseState.getVariable("var1"), *deps.vars.begin());
}

TEST(ExpressionObjectDependencies, LocalMapVariablesShouldBeFilteredOutOfDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    expCtx->variablesParseState.defineVariable("var1");
    auto mapSpec = BSON("$map" << BSON("input"
                                       << "$field1"
                                       << "as"
                                       << "var2"
                                       << "in"
                                       << BSON("$multiply" << BSON_ARRAY("$$var1"
                                                                         << "$$var2"))));

    auto expressionMap =
        ExpressionMap::parse(expCtx, mapSpec.firstElement(), expCtx->variablesParseState);
    DepsTracker deps;
    expressionMap->addDependencies(&deps);
    ASSERT_EQ(deps.vars.size(), 1UL);
    ASSERT_EQ(expCtx->variablesParseState.getVariable("var1"), *deps.vars.begin());
}

TEST(ExpressionObjectDependencies, LocalFilterVariablesShouldBeFilteredOutOfDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    expCtx->variablesParseState.defineVariable("var1");
    auto filterSpec = BSON("$filter" << BSON("input" << BSON_ARRAY(1 << 2 << 3) << "as"
                                                     << "var2"
                                                     << "cond"
                                                     << BSON("$gt" << BSON_ARRAY("$$var1"
                                                                                 << "$$var2"))));

    auto expressionFilter =
        ExpressionFilter::parse(expCtx, filterSpec.firstElement(), expCtx->variablesParseState);
    DepsTracker deps;
    expressionFilter->addDependencies(&deps);
    ASSERT_EQ(deps.vars.size(), 1UL);
    ASSERT_EQ(expCtx->variablesParseState.getVariable("var1"), *deps.vars.begin());
}

//
// Optimizations.
//

TEST(ExpressionObjectOptimizations, OptimizingAnObjectShouldOptimizeSubExpressions) {
    // Build up the object {a: {$add: [1, 2]}}.
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto addExpression =
        ExpressionAdd::parse(expCtx, BSON("$add" << BSON_ARRAY(1 << 2)).firstElement(), vps);
    auto object = expressionObjectCreateHelper(expCtx, {{"a", addExpression}});
    ASSERT_EQ(object->getChildExpressions().size(), 1UL);

    auto optimized = object->optimize();
    auto optimizedObject = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_TRUE(optimizedObject);
    ASSERT_VALUE_EQ(optimizedObject->evaluate(Document()), Value(BSON("a" << 3)));
};

TEST(ExpressionObjectOptimizations,
     OptimizingAnObjectWithAllConstantsShouldOptimizeToExpressionConstant) {

    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    // All constants should optimize to ExpressionConstant.
    auto objectWithAllConstants = ExpressionObject::parse(expCtx, BSON("b" << 1 << "c" << 1), vps);
    auto optimizedToAllConstants = objectWithAllConstants->optimize();
    auto constants = dynamic_cast<ExpressionConstant*>(optimizedToAllConstants.get());
    ASSERT_TRUE(constants);

    // Not all constants should not optimize to ExpressionConstant.
    auto objectNotAllConstants = ExpressionObject::parse(expCtx,
                                                         BSON("b" << 1 << "input"
                                                                  << "$inputField"),
                                                         vps);
    auto optimizedNotAllConstants = objectNotAllConstants->optimize();
    auto shouldNotBeConstant = dynamic_cast<ExpressionConstant*>(optimizedNotAllConstants.get());
    ASSERT_FALSE(shouldNotBeConstant);

    // Sub expression should optimize to constant expression.
    auto expressionWithConstantObject = ExpressionObject::parse(
        expCtx,
        BSON("willBeConstant" << BSON("$add" << BSON_ARRAY(1 << 2)) << "alreadyConstant"
                              << "string"),
        vps);
    auto optimizedWithConstant = expressionWithConstantObject->optimize();
    auto optimizedObject = dynamic_cast<ExpressionConstant*>(optimizedWithConstant.get());
    ASSERT_TRUE(optimizedObject);
    ASSERT_VALUE_EQ(optimizedObject->evaluate(Document()),
                    Value(BSON("willBeConstant" << 3 << "alreadyConstant"
                                                << "string")));
};

}  // namespace Object

namespace Or {

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObject = BSON("" << spec());
        BSONElement specElement = specObject.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult()),
                          toBson(expression->evaluate(fromBson(BSON("a" << 1)))));
        intrusive_ptr<Expression> optimized = expression->optimize();
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult()),
                          toBson(optimized->evaluate(fromBson(BSON("a" << 1)))));
    }

protected:
    virtual BSONObj spec() = 0;
    virtual bool expectedResult() = 0;
};

class OptimizeBase {
public:
    virtual ~OptimizeBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObject = BSON("" << spec());
        BSONElement specElement = specObject.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        intrusive_ptr<Expression> optimized = expression->optimize();
        ASSERT_BSONOBJ_EQ(expectedOptimized(), expressionToBson(optimized));
    }

protected:
    virtual BSONObj spec() = 0;
    virtual BSONObj expectedOptimized() = 0;
};

class NoOptimizeBase : public OptimizeBase {
    BSONObj expectedOptimized() {
        return constify(spec());
    }
};

/** $or without operands. */
class NoOperands : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSONArray());
    }
    bool expectedResult() {
        return false;
    }
};

/** $or passed 'true'. */
class True : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(true));
    }
    bool expectedResult() {
        return true;
    }
};

/** $or passed 'false'. */
class False : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $or passed 'true', 'true'. */
class TrueTrue : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(true << true));
    }
    bool expectedResult() {
        return true;
    }
};

/** $or passed 'true', 'false'. */
class TrueFalse : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(true << false));
    }
    bool expectedResult() {
        return true;
    }
};

/** $or passed 'false', 'true'. */
class FalseTrue : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(false << true));
    }
    bool expectedResult() {
        return true;
    }
};

/** $or passed 'false', 'false'. */
class FalseFalse : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(false << false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $or passed 'false', 'false', 'false'. */
class FalseFalseFalse : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(false << false << false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $or passed 'false', 'false', 'true'. */
class FalseFalseTrue : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(false << false << true));
    }
    bool expectedResult() {
        return true;
    }
};

/** $or passed '0', '1'. */
class ZeroOne : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(0 << 1));
    }
    bool expectedResult() {
        return true;
    }
};

/** $or passed '0', 'false'. */
class ZeroFalse : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(0 << false));
    }
    bool expectedResult() {
        return false;
    }
};

/** $or passed a field path. */
class FieldPath : public ExpectedResultBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY("$a"));
    }
    bool expectedResult() {
        return true;
    }
};

/** A constant expression is optimized to a constant. */
class OptimizeConstantExpression : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(1));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

/** A non constant expression is not optimized. */
class NonConstant : public NoOptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY("$a"));
    }
};

/** An expression beginning with a single constant is optimized. */
class ConstantNonConstantTrue : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(1 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

/** An expression beginning with a single constant is optimized. */
class ConstantNonConstantFalse : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(0 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
    // note: using $and as serialization of ExpressionCoerceToBool rather than
    // ExpressionAnd
};

/** An expression with a field path and '1'. */
class NonConstantOne : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY("$a" << 1));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

/** An expression with a field path and '0'. */
class NonConstantZero : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY("$a" << 0));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
};

/** An expression with two field paths and '1'. */
class NonConstantNonConstantOne : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY("$a"
                                        << "$b"
                                        << 1));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

/** An expression with two field paths and '0'. */
class NonConstantNonConstantZero : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY("$a"
                                        << "$b"
                                        << 0));
    }
    BSONObj expectedOptimized() {
        return BSON("$or" << BSON_ARRAY("$a"
                                        << "$b"));
    }
};

/** An expression with '0', '1', and a field path. */
class ZeroOneNonConstant : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(0 << 1 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

/** An expression with '0', '0', and a field path. */
class ZeroZeroNonConstant : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(0 << 0 << "$a"));
    }
    BSONObj expectedOptimized() {
        return BSON("$and" << BSON_ARRAY("$a"));
    }
};

/** Nested $or expressions. */
class Nested : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(0 << BSON("$or" << BSON_ARRAY(0)) << "$a"
                                          << "$b"));
    }
    BSONObj expectedOptimized() {
        return BSON("$or" << BSON_ARRAY("$a"
                                        << "$b"));
    }
};

/** Nested $or expressions containing a nested value evaluating to false. */
class NestedOne : public OptimizeBase {
    BSONObj spec() {
        return BSON("$or" << BSON_ARRAY(0 << BSON("$or" << BSON_ARRAY(BSON("$or" << BSON_ARRAY(1))))
                                          << "$a"
                                          << "$b"));
    }
    BSONObj expectedOptimized() {
        return BSON("$const" << true);
    }
};

}  // namespace Or

namespace Parse {

namespace Object {

/**
 * Parses the object given by 'specification', with the options given by 'parseContextOptions'.
 */
boost::intrusive_ptr<Expression> parseObject(BSONObj specification) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    return Expression::parseObject(expCtx, specification, vps);
};

TEST(ParseObject, ShouldAcceptEmptyObject) {
    auto resultExpression = parseObject(BSONObj());

    // Should return an empty ExpressionObject.
    auto resultObject = dynamic_cast<ExpressionObject*>(resultExpression.get());
    ASSERT_TRUE(resultObject);

    ASSERT_EQ(resultObject->getChildExpressions().size(), 0UL);
}

TEST(ParseObject, ShouldRecognizeKnownExpression) {
    auto resultExpression = parseObject(BSON("$and" << BSONArray()));

    // Should return an ExpressionAnd.
    auto resultAnd = dynamic_cast<ExpressionAnd*>(resultExpression.get());
    ASSERT_TRUE(resultAnd);
}

}  // namespace Object

namespace Expression {

using mongo::Expression;

/**
 * Parses an expression from the given BSON specification.
 */
boost::intrusive_ptr<Expression> parseExpression(BSONObj specification) {
    const boost::intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    return Expression::parseExpression(expCtx, specification, vps);
}

TEST(ParseExpression, ShouldRecognizeConstExpression) {
    auto resultExpression = parseExpression(BSON("$const" << 5));
    auto constExpression = dynamic_cast<ExpressionConstant*>(resultExpression.get());
    ASSERT_TRUE(constExpression);
    ASSERT_VALUE_EQ(constExpression->serialize(false), Value(Document{{"$const", 5}}));
}

TEST(ParseExpression, ShouldRejectUnknownExpression) {
    ASSERT_THROWS(parseExpression(BSON("$invalid" << 1)), AssertionException);
}

TEST(ParseExpression, ShouldRejectExpressionArgumentsWhichAreNotInArray) {
    ASSERT_THROWS(parseExpression(BSON("$strcasecmp"
                                       << "foo")),
                  AssertionException);
}

TEST(ParseExpression, ShouldRejectExpressionWithWrongNumberOfArguments) {
    ASSERT_THROWS(parseExpression(BSON("$strcasecmp" << BSON_ARRAY("foo"))), AssertionException);
}

TEST(ParseExpression, ShouldRejectObjectWithTwoTopLevelExpressions) {
    ASSERT_THROWS(parseExpression(BSON("$and" << BSONArray() << "$or" << BSONArray())),
                  AssertionException);
}

TEST(ParseExpression, ShouldRejectExpressionIfItsNotTheOnlyField) {
    ASSERT_THROWS(parseExpression(BSON("$and" << BSONArray() << "a" << BSON("$or" << BSONArray()))),
                  AssertionException);
}

TEST(ParseExpression, ShouldParseExpressionWithMultipleArguments) {
    auto resultExpression = parseExpression(BSON("$strcasecmp" << BSON_ARRAY("foo"
                                                                             << "FOO")));
    auto strCaseCmpExpression = dynamic_cast<ExpressionStrcasecmp*>(resultExpression.get());
    ASSERT_TRUE(strCaseCmpExpression);
    vector<Value> arguments = {Value(Document{{"$const", "foo"_sd}}),
                               Value(Document{{"$const", "FOO"_sd}})};
    ASSERT_VALUE_EQ(strCaseCmpExpression->serialize(false),
                    Value(Document{{"$strcasecmp", arguments}}));
}

TEST(ParseExpression, ShouldParseExpressionWithNoArguments) {
    auto resultExpression = parseExpression(BSON("$and" << BSONArray()));
    auto andExpression = dynamic_cast<ExpressionAnd*>(resultExpression.get());
    ASSERT_TRUE(andExpression);
    ASSERT_VALUE_EQ(andExpression->serialize(false), Value(Document{{"$and", vector<Value>{}}}));
}

TEST(ParseExpression, ShouldParseExpressionWithOneArgument) {
    auto resultExpression = parseExpression(BSON("$and" << BSON_ARRAY(1)));
    auto andExpression = dynamic_cast<ExpressionAnd*>(resultExpression.get());
    ASSERT_TRUE(andExpression);
    vector<Value> arguments = {Value(Document{{"$const", 1}})};
    ASSERT_VALUE_EQ(andExpression->serialize(false), Value(Document{{"$and", arguments}}));
}

TEST(ParseExpression, ShouldAcceptArgumentWithoutArrayForVariadicExpressions) {
    auto resultExpression = parseExpression(BSON("$and" << 1));
    auto andExpression = dynamic_cast<ExpressionAnd*>(resultExpression.get());
    ASSERT_TRUE(andExpression);
    vector<Value> arguments = {Value(Document{{"$const", 1}})};
    ASSERT_VALUE_EQ(andExpression->serialize(false), Value(Document{{"$and", arguments}}));
}

TEST(ParseExpression, ShouldAcceptArgumentWithoutArrayAsSingleArgument) {
    auto resultExpression = parseExpression(BSON("$not" << 1));
    auto notExpression = dynamic_cast<ExpressionNot*>(resultExpression.get());
    ASSERT_TRUE(notExpression);
    vector<Value> arguments = {Value(Document{{"$const", 1}})};
    ASSERT_VALUE_EQ(notExpression->serialize(false), Value(Document{{"$not", arguments}}));
}

TEST(ParseExpression, ShouldAcceptObjectAsSingleArgument) {
    auto resultExpression = parseExpression(BSON("$and" << BSON("$const" << 1)));
    auto andExpression = dynamic_cast<ExpressionAnd*>(resultExpression.get());
    ASSERT_TRUE(andExpression);
    vector<Value> arguments = {Value(Document{{"$const", 1}})};
    ASSERT_VALUE_EQ(andExpression->serialize(false), Value(Document{{"$and", arguments}}));
}

TEST(ParseExpression, ShouldAcceptObjectInsideArrayAsSingleArgument) {
    auto resultExpression = parseExpression(BSON("$and" << BSON_ARRAY(BSON("$const" << 1))));
    auto andExpression = dynamic_cast<ExpressionAnd*>(resultExpression.get());
    ASSERT_TRUE(andExpression);
    vector<Value> arguments = {Value(Document{{"$const", 1}})};
    ASSERT_VALUE_EQ(andExpression->serialize(false), Value(Document{{"$and", arguments}}));
}

}  // namespace Expression

namespace Operand {

using mongo::Expression;

/**
 * Parses an operand from the given BSON specification. The field name is ignored, since it is
 * assumed to have come from an array, or to have been the only argument to an expression, in which
 * case the field name would be the name of the expression.
 */
intrusive_ptr<Expression> parseOperand(BSONObj specification) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    BSONElement specElement = specification.firstElement();
    VariablesParseState vps = expCtx->variablesParseState;
    return Expression::parseOperand(expCtx, specElement, vps);
}

TEST(ParseOperand, ShouldRecognizeFieldPath) {
    auto resultExpression = parseOperand(BSON(""
                                              << "$field"));
    auto fieldPathExpression = dynamic_cast<ExpressionFieldPath*>(resultExpression.get());
    ASSERT_TRUE(fieldPathExpression);
    ASSERT_VALUE_EQ(fieldPathExpression->serialize(false), Value("$field"_sd));
}

TEST(ParseOperand, ShouldRecognizeStringLiteral) {
    auto resultExpression = parseOperand(BSON(""
                                              << "foo"));
    auto constantExpression = dynamic_cast<ExpressionConstant*>(resultExpression.get());
    ASSERT_TRUE(constantExpression);
    ASSERT_VALUE_EQ(constantExpression->serialize(false), Value(Document{{"$const", "foo"_sd}}));
}

TEST(ParseOperand, ShouldRecognizeNestedArray) {
    auto resultExpression = parseOperand(BSON("" << BSON_ARRAY("foo"
                                                               << "$field")));
    auto arrayExpression = dynamic_cast<ExpressionArray*>(resultExpression.get());
    ASSERT_TRUE(arrayExpression);
    vector<Value> expectedSerializedArray = {Value(Document{{"$const", "foo"_sd}}),
                                             Value("$field"_sd)};
    ASSERT_VALUE_EQ(arrayExpression->serialize(false), Value(expectedSerializedArray));
}

TEST(ParseOperand, ShouldRecognizeNumberLiteral) {
    auto resultExpression = parseOperand(BSON("" << 5));
    auto constantExpression = dynamic_cast<ExpressionConstant*>(resultExpression.get());
    ASSERT_TRUE(constantExpression);
    ASSERT_VALUE_EQ(constantExpression->serialize(false), Value(Document{{"$const", 5}}));
}

TEST(ParseOperand, ShouldRecognizeNestedExpression) {
    auto resultExpression = parseOperand(BSON("" << BSON("$and" << BSONArray())));
    auto andExpression = dynamic_cast<ExpressionAnd*>(resultExpression.get());
    ASSERT_TRUE(andExpression);
    ASSERT_VALUE_EQ(andExpression->serialize(false), Value(Document{{"$and", vector<Value>{}}}));
}

}  // namespace Operand

}  // namespace Parse

namespace Set {
Value sortSet(Value set) {
    if (set.nullish()) {
        return Value(BSONNULL);
    }
    vector<Value> sortedSet = set.getArray();
    ValueComparator valueComparator;
    sort(sortedSet.begin(), sortedSet.end(), valueComparator.getLessThan());
    return Value(sortedSet);
}

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        const Document spec = getSpec();
        const Value args = spec["input"];
        if (!spec["expected"].missing()) {
            FieldIterator fields(spec["expected"].getDocument());
            while (fields.more()) {
                const Document::FieldPair field(fields.next());
                const Value expected = field.second;
                const BSONObj obj = BSON(field.first << args);
                VariablesParseState vps = expCtx->variablesParseState;
                const intrusive_ptr<Expression> expr =
                    Expression::parseExpression(expCtx, obj, vps);
                Value result = expr->evaluate(Document());
                if (result.getType() == Array) {
                    result = sortSet(result);
                }
                if (ValueComparator().evaluate(result != expected)) {
                    string errMsg = str::stream()
                        << "for expression " << field.first.toString() << " with argument "
                        << args.toString() << " full tree: " << expr->serialize(false).toString()
                        << " expected: " << expected.toString()
                        << " but got: " << result.toString();
                    FAIL(errMsg);
                }
                // TODO test optimize here
            }
        }
        if (!spec["error"].missing()) {
            const vector<Value>& asserters = spec["error"].getArray();
            size_t n = asserters.size();
            for (size_t i = 0; i < n; i++) {
                const BSONObj obj = BSON(asserters[i].getString() << args);
                VariablesParseState vps = expCtx->variablesParseState;
                ASSERT_THROWS(
                    [&] {
                        // NOTE: parse and evaluatation failures are treated the
                        // same
                        const intrusive_ptr<Expression> expr =
                            Expression::parseExpression(expCtx, obj, vps);
                        expr->evaluate(Document());
                    }(),
                    AssertionException);
            }
        }
    }

private:
    virtual Document getSpec() = 0;
};

class Same : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << DOC_ARRAY(1 << 2)) << "expected"
                           << DOC("$setIsSubset" << true << "$setEquals" << true
                                                 << "$setIntersection"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setDifference"
                                                 << vector<Value>()));
    }
};

class Redundant : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << DOC_ARRAY(1 << 2 << 2)) << "expected"
                           << DOC("$setIsSubset" << true << "$setEquals" << true
                                                 << "$setIntersection"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setDifference"
                                                 << vector<Value>()));
    }
};

class DoubleRedundant : public ExpectedResultBase {
    Document getSpec() {
        return DOC(
            "input" << DOC_ARRAY(DOC_ARRAY(1 << 1 << 2) << DOC_ARRAY(1 << 2 << 2)) << "expected"
                    << DOC("$setIsSubset" << true << "$setEquals" << true << "$setIntersection"
                                          << DOC_ARRAY(1 << 2)
                                          << "$setUnion"
                                          << DOC_ARRAY(1 << 2)
                                          << "$setDifference"
                                          << vector<Value>()));
    }
};

class Super : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << DOC_ARRAY(1)) << "expected"
                           << DOC("$setIsSubset" << false << "$setEquals" << false
                                                 << "$setIntersection"
                                                 << DOC_ARRAY(1)
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setDifference"
                                                 << DOC_ARRAY(2)));
    }
};

class SuperWithRedundant : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2 << 2) << DOC_ARRAY(1)) << "expected"
                           << DOC("$setIsSubset" << false << "$setEquals" << false
                                                 << "$setIntersection"
                                                 << DOC_ARRAY(1)
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setDifference"
                                                 << DOC_ARRAY(2)));
    }
};

class Sub : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1) << DOC_ARRAY(1 << 2)) << "expected"
                           << DOC("$setIsSubset" << true << "$setEquals" << false
                                                 << "$setIntersection"
                                                 << DOC_ARRAY(1)
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setDifference"
                                                 << vector<Value>()));
    }
};

class SameBackwards : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << DOC_ARRAY(2 << 1)) << "expected"
                           << DOC("$setIsSubset" << true << "$setEquals" << true
                                                 << "$setIntersection"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2)
                                                 << "$setDifference"
                                                 << vector<Value>()));
    }
};

class NoOverlap : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << DOC_ARRAY(8 << 4)) << "expected"
                           << DOC("$setIsSubset" << false << "$setEquals" << false
                                                 << "$setIntersection"
                                                 << vector<Value>()
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2 << 4 << 8)
                                                 << "$setDifference"
                                                 << DOC_ARRAY(1 << 2)));
    }
};

class Overlap : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << DOC_ARRAY(8 << 2 << 4)) << "expected"
                           << DOC("$setIsSubset" << false << "$setEquals" << false
                                                 << "$setIntersection"
                                                 << DOC_ARRAY(2)
                                                 << "$setUnion"
                                                 << DOC_ARRAY(1 << 2 << 4 << 8)
                                                 << "$setDifference"
                                                 << DOC_ARRAY(1)));
    }
};

class LastNull : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << Value(BSONNULL)) << "expected"
                           << DOC("$setIntersection" << BSONNULL << "$setUnion" << BSONNULL
                                                     << "$setDifference"
                                                     << BSONNULL)
                           << "error"
                           << DOC_ARRAY("$setEquals"_sd
                                        << "$setIsSubset"_sd));
    }
};

class FirstNull : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(Value(BSONNULL) << DOC_ARRAY(1 << 2)) << "expected"
                           << DOC("$setIntersection" << BSONNULL << "$setUnion" << BSONNULL
                                                     << "$setDifference"
                                                     << BSONNULL)
                           << "error"
                           << DOC_ARRAY("$setEquals"_sd
                                        << "$setIsSubset"_sd));
    }
};

class NoArg : public ExpectedResultBase {
    Document getSpec() {
        return DOC(
            "input" << vector<Value>() << "expected"
                    << DOC("$setIntersection" << vector<Value>() << "$setUnion" << vector<Value>())
                    << "error"
                    << DOC_ARRAY("$setEquals"_sd
                                 << "$setIsSubset"_sd
                                 << "$setDifference"_sd));
    }
};

class OneArg : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2)) << "expected"
                           << DOC("$setIntersection" << DOC_ARRAY(1 << 2) << "$setUnion"
                                                     << DOC_ARRAY(1 << 2))
                           << "error"
                           << DOC_ARRAY("$setEquals"_sd
                                        << "$setIsSubset"_sd
                                        << "$setDifference"_sd));
    }
};

class EmptyArg : public ExpectedResultBase {
    Document getSpec() {
        return DOC(
            "input" << DOC_ARRAY(vector<Value>()) << "expected"
                    << DOC("$setIntersection" << vector<Value>() << "$setUnion" << vector<Value>())
                    << "error"
                    << DOC_ARRAY("$setEquals"_sd
                                 << "$setIsSubset"_sd
                                 << "$setDifference"_sd));
    }
};

class LeftArgEmpty : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(vector<Value>() << DOC_ARRAY(1 << 2)) << "expected"
                           << DOC("$setIntersection" << vector<Value>() << "$setUnion"
                                                     << DOC_ARRAY(1 << 2)
                                                     << "$setIsSubset"
                                                     << true
                                                     << "$setEquals"
                                                     << false
                                                     << "$setDifference"
                                                     << vector<Value>()));
    }
};

class RightArgEmpty : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2) << vector<Value>()) << "expected"
                           << DOC("$setIntersection" << vector<Value>() << "$setUnion"
                                                     << DOC_ARRAY(1 << 2)
                                                     << "$setIsSubset"
                                                     << false
                                                     << "$setEquals"
                                                     << false
                                                     << "$setDifference"
                                                     << DOC_ARRAY(1 << 2)));
    }
};

class ManyArgs : public ExpectedResultBase {
    Document getSpec() {
        return DOC(
            "input" << DOC_ARRAY(DOC_ARRAY(8 << 3) << DOC_ARRAY("asdf"_sd
                                                                << "foo"_sd)
                                                   << DOC_ARRAY(80.3 << 34)
                                                   << vector<Value>()
                                                   << DOC_ARRAY(80.3 << "foo"_sd << 11 << "yay"_sd))
                    << "expected"
                    << DOC("$setIntersection" << vector<Value>() << "$setEquals" << false
                                              << "$setUnion"
                                              << DOC_ARRAY(3 << 8 << 11 << 34 << 80.3 << "asdf"_sd
                                                             << "foo"_sd
                                                             << "yay"_sd))
                    << "error"
                    << DOC_ARRAY("$setIsSubset"_sd
                                 << "$setDifference"_sd));
    }
};

class ManyArgsEqual : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1 << 2 << 4) << DOC_ARRAY(1 << 2 << 2 << 4)
                                                               << DOC_ARRAY(4 << 1 << 2)
                                                               << DOC_ARRAY(2 << 1 << 1 << 4))
                           << "expected"
                           << DOC("$setIntersection" << DOC_ARRAY(1 << 2 << 4) << "$setEquals"
                                                     << true
                                                     << "$setUnion"
                                                     << DOC_ARRAY(1 << 2 << 4))
                           << "error"
                           << DOC_ARRAY("$setIsSubset"_sd
                                        << "$setDifference"_sd));
    }
};
}  // namespace Set

namespace Strcasecmp {

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        assertResult(expectedResult(), spec());
        assertResult(-expectedResult(), reverseSpec());
    }

protected:
    virtual string a() = 0;
    virtual string b() = 0;
    virtual int expectedResult() = 0;

private:
    BSONObj spec() {
        return BSON("$strcasecmp" << BSON_ARRAY(a() << b()));
    }
    BSONObj reverseSpec() {
        return BSON("$strcasecmp" << BSON_ARRAY(b() << a()));
    }
    void assertResult(int expectedResult, const BSONObj& spec) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObj = BSON("" << spec);
        BSONElement specElement = specObj.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec), expressionToBson(expression));
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult), toBson(expression->evaluate(Document())));
    }
};

class NullBegin : public ExpectedResultBase {
    string a() {
        return string("\0ab", 3);
    }
    string b() {
        return string("\0AB", 3);
    }
    int expectedResult() {
        return 0;
    }
};

class NullEnd : public ExpectedResultBase {
    string a() {
        return string("ab\0", 3);
    }
    string b() {
        return string("aB\0", 3);
    }
    int expectedResult() {
        return 0;
    }
};

class NullMiddleLt : public ExpectedResultBase {
    string a() {
        return string("a\0a", 3);
    }
    string b() {
        return string("a\0B", 3);
    }
    int expectedResult() {
        return -1;
    }
};

class NullMiddleEq : public ExpectedResultBase {
    string a() {
        return string("a\0b", 3);
    }
    string b() {
        return string("a\0B", 3);
    }
    int expectedResult() {
        return 0;
    }
};

class NullMiddleGt : public ExpectedResultBase {
    string a() {
        return string("a\0c", 3);
    }
    string b() {
        return string("a\0B", 3);
    }
    int expectedResult() {
        return 1;
    }
};

}  // namespace Strcasecmp

namespace StrLenBytes {

TEST(ExpressionStrLenBytes, ComputesLengthOfString) {
    assertExpectedResults("$strLenBytes", {{{Value("abc"_sd)}, Value(3)}});
}

TEST(ExpressionStrLenBytes, ComputesLengthOfEmptyString) {
    assertExpectedResults("$strLenBytes", {{{Value(StringData())}, Value(0)}});
}

TEST(ExpressionStrLenBytes, ComputesLengthOfStringWithNull) {
    assertExpectedResults("$strLenBytes", {{{Value("ab\0c"_sd)}, Value(4)}});
}

TEST(ExpressionStrLenCP, ComputesLengthOfStringWithNullAtEnd) {
    assertExpectedResults("$strLenBytes", {{{Value("abc\0"_sd)}, Value(4)}});
}

}  // namespace StrLenBytes

namespace StrLenCP {

TEST(ExpressionStrLenCP, ComputesLengthOfASCIIString) {
    assertExpectedResults("$strLenCP", {{{Value("abc"_sd)}, Value(3)}});
}

TEST(ExpressionStrLenCP, ComputesLengthOfEmptyString) {
    assertExpectedResults("$strLenCP", {{{Value(StringData())}, Value(0)}});
}

TEST(ExpressionStrLenCP, ComputesLengthOfStringWithNull) {
    assertExpectedResults("$strLenCP", {{{Value("ab\0c"_sd)}, Value(4)}});
}

TEST(ExpressionStrLenCP, ComputesLengthOfStringWithNullAtEnd) {
    assertExpectedResults("$strLenCP", {{{Value("abc\0"_sd)}, Value(4)}});
}

TEST(ExpressionStrLenCP, ComputesLengthOfStringWithAccent) {
    assertExpectedResults("$strLenCP", {{{Value("a\0bâ"_sd)}, Value(4)}});
}

TEST(ExpressionStrLenCP, ComputesLengthOfStringWithSpecialCharacters) {
    assertExpectedResults("$strLenCP", {{{Value("ºabøåß"_sd)}, Value(6)}});
}

}  // namespace StrLenCP

namespace SubstrBytes {

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObj = BSON("" << spec());
        BSONElement specElement = specObj.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult()), toBson(expression->evaluate(Document())));
    }

protected:
    virtual string str() = 0;
    virtual int offset() = 0;
    virtual int length() = 0;
    virtual string expectedResult() = 0;

private:
    BSONObj spec() {
        return BSON("$substrBytes" << BSON_ARRAY(str() << offset() << length()));
    }
};

/** Retrieve a full string containing a null character. */
class FullNull : public ExpectedResultBase {
    string str() {
        return string("a\0b", 3);
    }
    int offset() {
        return 0;
    }
    int length() {
        return 3;
    }
    string expectedResult() {
        return str();
    }
};

/** Retrieve a substring beginning with a null character. */
class BeginAtNull : public ExpectedResultBase {
    string str() {
        return string("a\0b", 3);
    }
    int offset() {
        return 1;
    }
    int length() {
        return 2;
    }
    string expectedResult() {
        return string("\0b", 2);
    }
};

/** Retrieve a substring ending with a null character. */
class EndAtNull : public ExpectedResultBase {
    string str() {
        return string("a\0b", 3);
    }
    int offset() {
        return 0;
    }
    int length() {
        return 2;
    }
    string expectedResult() {
        return string("a\0", 2);
    }
};

/** Drop a beginning null character. */
class DropBeginningNull : public ExpectedResultBase {
    string str() {
        return string("\0b", 2);
    }
    int offset() {
        return 1;
    }
    int length() {
        return 1;
    }
    string expectedResult() {
        return "b";
    }
};

/** Drop an ending null character. */
class DropEndingNull : public ExpectedResultBase {
    string str() {
        return string("a\0", 2);
    }
    int offset() {
        return 0;
    }
    int length() {
        return 1;
    }
    string expectedResult() {
        return "a";
    }
};

/** When length is negative, the remainder of the string should be returned. */
class NegativeLength : public ExpectedResultBase {
    string str() {
        return string("abcdefghij");
    }
    int offset() {
        return 2;
    }
    int length() {
        return -1;
    }
    string expectedResult() {
        return "cdefghij";
    }
};

TEST(ExpressionSubstrTest, ThrowsWithNegativeStart) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    const auto str = "abcdef"_sd;
    const auto expr =
        Expression::parseExpression(expCtx, BSON("$substrCP" << BSON_ARRAY(str << -5 << 1)), vps);
    ASSERT_THROWS([&] { expr->evaluate(Document()); }(), AssertionException);
}

}  // namespace Substr

namespace SubstrCP {

TEST(ExpressionSubstrCPTest, DoesThrowWithBadContinuationByte) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    const auto continuationByte = "\x80\x00"_sd;
    const auto expr = Expression::parseExpression(
        expCtx, BSON("$substrCP" << BSON_ARRAY(continuationByte << 0 << 1)), vps);
    ASSERT_THROWS([&] { expr->evaluate(Document()); }(), AssertionException);
}

TEST(ExpressionSubstrCPTest, DoesThrowWithInvalidLeadingByte) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;

    const auto leadingByte = "\xFF\x00"_sd;
    const auto expr = Expression::parseExpression(
        expCtx, BSON("$substrCP" << BSON_ARRAY(leadingByte << 0 << 1)), vps);
    ASSERT_THROWS([&] { expr->evaluate(Document()); }(), AssertionException);
}

TEST(ExpressionSubstrCPTest, WithStandardValue) {
    assertExpectedResults("$substrCP", {{{Value("abc"_sd), Value(0), Value(2)}, Value("ab"_sd)}});
}

TEST(ExpressionSubstrCPTest, WithNullCharacter) {
    assertExpectedResults("$substrCP",
                          {{{Value("abc\0d"_sd), Value(2), Value(3)}, Value("c\0d"_sd)}});
}

TEST(ExpressionSubstrCPTest, WithNullCharacterAtEnd) {
    assertExpectedResults("$substrCP",
                          {{{Value("abc\0"_sd), Value(2), Value(2)}, Value("c\0"_sd)}});
}

TEST(ExpressionSubstrCPTest, WithOutOfRangeString) {
    assertExpectedResults("$substrCP",
                          {{{Value("abc"_sd), Value(3), Value(2)}, Value(StringData())}});
}

TEST(ExpressionSubstrCPTest, WithPartiallyOutOfRangeString) {
    assertExpectedResults("$substrCP", {{{Value("abc"_sd), Value(1), Value(4)}, Value("bc"_sd)}});
}

TEST(ExpressionSubstrCPTest, WithUnicodeValue) {
    assertExpectedResults("$substrCP",
                          {{{Value("øø∫å"_sd), Value(0), Value(4)}, Value("øø∫å"_sd)}});
    assertExpectedResults("$substrBytes",
                          {{{Value("øø∫å"_sd), Value(0), Value(4)}, Value("øø"_sd)}});
}

TEST(ExpressionSubstrCPTest, WithMixedUnicodeAndASCIIValue) {
    assertExpectedResults("$substrCP",
                          {{{Value("a∫bøßabc"_sd), Value(1), Value(4)}, Value("∫bøß"_sd)}});
    assertExpectedResults("$substrBytes",
                          {{{Value("a∫bøßabc"_sd), Value(1), Value(4)}, Value("∫b"_sd)}});
}

TEST(ExpressionSubstrCPTest, ShouldCoerceDateToString) {
    assertExpectedResults("$substrCP",
                          {{{Value(Date_t::fromMillisSinceEpoch(0)), Value(0), Value(1000)},
                            Value("1970-01-01T00:00:00.000Z"_sd)}});
    assertExpectedResults("$substrBytes",
                          {{{Value(Date_t::fromMillisSinceEpoch(0)), Value(0), Value(1000)},
                            Value("1970-01-01T00:00:00.000Z"_sd)}});
}

}  // namespace SubstrCP

namespace Trim {

TEST(ExpressionTrimParsingTest, ThrowsIfSpecIsNotAnObject) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    ASSERT_THROWS(
        Expression::parseExpression(expCtx, BSON("$trim" << 1), expCtx->variablesParseState),
        AssertionException);
    ASSERT_THROWS(Expression::parseExpression(
                      expCtx, BSON("$trim" << BSON_ARRAY(1 << 2)), expCtx->variablesParseState),
                  AssertionException);
    ASSERT_THROWS(Expression::parseExpression(
                      expCtx, BSON("$ltrim" << BSONNULL), expCtx->variablesParseState),
                  AssertionException);
    ASSERT_THROWS(Expression::parseExpression(expCtx,
                                              BSON("$rtrim"
                                                   << "string"),
                                              expCtx->variablesParseState),
                  AssertionException);
}

TEST(ExpressionTrimParsingTest, ThrowsIfSpecDoesNotSpecifyInput) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    ASSERT_THROWS(Expression::parseExpression(
                      expCtx, BSON("$trim" << BSONObj()), expCtx->variablesParseState),
                  AssertionException);
    ASSERT_THROWS(Expression::parseExpression(expCtx,
                                              BSON("$ltrim" << BSON("chars"
                                                                    << "xyz")),
                                              expCtx->variablesParseState),
                  AssertionException);
}

TEST(ExpressionTrimParsingTest, ThrowsIfSpecContainsUnrecognizedField) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    ASSERT_THROWS(Expression::parseExpression(
                      expCtx, BSON("$trim" << BSON("other" << 1)), expCtx->variablesParseState),
                  AssertionException);
    ASSERT_THROWS(Expression::parseExpression(expCtx,
                                              BSON("$ltrim" << BSON("chars"
                                                                    << "xyz"
                                                                    << "other"
                                                                    << 1)),
                                              expCtx->variablesParseState),
                  AssertionException);
    ASSERT_THROWS(Expression::parseExpression(expCtx,
                                              BSON("$rtrim" << BSON("input"
                                                                    << "$x"
                                                                    << "chars"
                                                                    << "xyz"
                                                                    << "other"
                                                                    << 1)),
                                              expCtx->variablesParseState),
                  AssertionException);
}

TEST(ExpressionTrimTest, ThrowsIfInputIsNotString) {
    ASSERT_THROWS(evaluateNamedArgExpression("$trim", Document{{"input", 1}}), AssertionException);
    ASSERT_THROWS(evaluateNamedArgExpression("$trim", Document{{"input", BSON_ARRAY(1 << 2)}}),
                  AssertionException);
    ASSERT_THROWS(evaluateNamedArgExpression("$ltrim", Document{{"input", 3}}), AssertionException);
    ASSERT_THROWS(evaluateNamedArgExpression("$rtrim", Document{{"input", Document{{"x", 1}}}}),
                  AssertionException);
}

TEST(ExpressionTrimTest, ThrowsIfCharsIsNotAString) {
    ASSERT_THROWS(evaluateNamedArgExpression("$trim", Document{{"input", " x "_sd}, {"chars", 1}}),
                  AssertionException);
    ASSERT_THROWS(evaluateNamedArgExpression(
                      "$trim", Document{{"input", " x "_sd}, {"chars", BSON_ARRAY(1 << 2)}}),
                  AssertionException);
    ASSERT_THROWS(evaluateNamedArgExpression("$ltrim", Document{{"input", " x "_sd}, {"chars", 3}}),
                  AssertionException);
    ASSERT_THROWS(evaluateNamedArgExpression(
                      "$rtrim", Document{{"input", " x "_sd}, {"chars", Document{{"x", 1}}}}),
                  AssertionException);
}

TEST(ExpressionTrimTest, DoesTrimAsciiWhitespace) {
    // Trim from both sides.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", "  abc  "_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", "\n  abc \r\n "_sd}}),
                    Value{"abc"_sd});

    // Trim just from the right.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "abc  "_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "abc \r\n "_sd}}),
                    Value{"abc"_sd});

    // Trim just from the left.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "  abc"_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "\n  abc"_sd}}),
                    Value{"abc"_sd});

    // Make sure we don't trim from the opposite side when doing $ltrim or $rtrim.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "  abc"_sd}}),
                    Value{"  abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "\t \nabc \r\n "_sd}}),
                    Value{"\t \nabc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "  abc  "_sd}}),
                    Value{"abc  "_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "\n  abc \t\n  "_sd}}),
                    Value{"abc \t\n  "_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "abc  "_sd}}),
                    Value{"abc  "_sd});
}

TEST(ExpressionTrimTest, DoesTrimNullCharacters) {
    // Trim from both sides.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", "\0\0abc\0"_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", "\0 \0 abc \0  "_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "\n \0  abc \r\0\n "_sd}}),
        Value{"abc"_sd});

    // Trim just from the right.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "abc\0\0"_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "abc \r\0\n\0 "_sd}}),
                    Value{"abc"_sd});

    // Trim just from the left.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "\0\0abc"_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "\n \0\0 abc"_sd}}),
                    Value{"abc"_sd});

    // Make sure we don't trim from the opposite side when doing $ltrim or $rtrim.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "\0\0abc"_sd}}),
                    Value{"\0\0abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", " \0 abc"_sd}}),
                    Value{" \0 abc"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "\t\0\0 \nabc \r\n "_sd}}),
        Value{"\t\0\0 \nabc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "  abc\0\0"_sd}}),
                    Value{"abc\0\0"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$ltrim", Document{{"input", "\n  abc \t\0\n \0\0 "_sd}}),
        Value{"abc \t\0\n \0\0 "_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "abc\0\0"_sd}}),
                    Value{"abc\0\0"_sd});
}

TEST(ExpressionTrimTest, DoesTrimUnicodeWhitespace) {
    // Trim from both sides.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "\u2001abc\u2004\u200A"_sd}}),
        Value{"abc"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$trim", Document{{"input", "\n\u0020 \0\u2007  abc \r\0\n\u0009\u200A "_sd}}),
        Value{"abc"_sd});

    // Trim just from the right.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "abc\u2007\u2006"_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$rtrim", Document{{"input", "abc \r\u2009\u0009\u200A\n\0 "_sd}}),
                    Value{"abc"_sd});

    // Trim just from the left.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "\u2009\u2004abc"_sd}}),
                    Value{"abc"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$ltrim", Document{{"input", "\n \u2000 \0\u2008\0 \u200Aabc"_sd}}),
                    Value{"abc"_sd});
}

TEST(ExpressionTrimTest, DoesTrimCustomAsciiCharacters) {
    // Trim from both sides.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "xxXXxx"_sd}, {"chars", "x"_sd}}),
        Value{"XX"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "00123"_sd}, {"chars", "0"_sd}}),
        Value{"123"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim",
                                   Document{{"input", "30:00:12 I don't care about the time"_sd},
                                            {"chars", "0123456789: "_sd}}),
        Value{"I don't care about the time"_sd});

    // Trim just from the right.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "xxXXxx"_sd}, {"chars", "x"_sd}}),
        Value{"xxXX"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "00123"_sd}, {"chars", "0"_sd}}),
        Value{"00123"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim",
                                   Document{{"input", "30:00:12 I don't care about the time"_sd},
                                            {"chars", "0123456789: "_sd}}),
        Value{"30:00:12 I don't care about the time"_sd});

    // Trim just from the left.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "xxXXxx"_sd}, {"chars", "x"_sd}}),
        Value{"xxXX"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "00123"_sd}, {"chars", "0"_sd}}),
        Value{"00123"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim",
                                   Document{{"input", "30:00:12 I don't care about the time"_sd},
                                            {"chars", "0123456789: "_sd}}),
        Value{"30:00:12 I don't care about the time"_sd});
}

TEST(ExpressionTrimTest, DoesTrimCustomUnicodeCharacters) {
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$ltrim", Document{{"input", "∃x.x ≥ y"_sd}, {"chars", "∃"_sd}}),
        Value{"x.x ≥ y"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "∃x.x ≥ y"_sd}, {"chars", "∃"_sd}}),
        Value{"∃x.x ≥ y"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "∃x.x ≥ y"_sd}, {"chars", "∃"_sd}}),
        Value{"x.x ≥ y"_sd});

    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$ltrim", Document{{"input", "⌊x⌋"_sd}, {"chars", "⌊⌋"_sd}}),
        Value{"x⌋"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "⌊x⌋"_sd}, {"chars", "⌊⌋"_sd}}),
        Value{"⌊x"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "⌊x⌋"_sd}, {"chars", "⌊⌋"_sd}}),
        Value{"x"_sd});
}

TEST(ExpressionTrimTest, DoesTrimCustomMixOfUnicodeAndAsciiCharacters) {
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$ltrim", Document{{"input", "∃x.x ≥ y"_sd}, {"chars", "∃y"_sd}}),
                    Value{"x.x ≥ y"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$rtrim", Document{{"input", "∃x.x ≥ y"_sd}, {"chars", "∃y"_sd}}),
                    Value{"∃x.x ≥ "_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "∃x.x ≥ y"_sd}, {"chars", "∃y"_sd}}),
        Value{"x.x ≥ "_sd});

    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$ltrim", Document{{"input", "⌊x⌋"_sd}, {"chars", "⌊x⌋"_sd}}),
        Value{""_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "⌊x⌋"_sd}, {"chars", "⌊x⌋"_sd}}),
        Value{""_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "⌊x⌋"_sd}, {"chars", "⌊x⌋"_sd}}),
        Value{""_sd});

    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$ltrim", Document{{"input", "▹▱◯□ I ▙◉VE Shapes □◯▱◃"_sd}, {"chars", "□◯▱◃▹ "_sd}}),
        Value{"I ▙◉VE Shapes □◯▱◃"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$rtrim", Document{{"input", "▹▱◯□ I ▙◉VE Shapes □◯▱◃"_sd}, {"chars", "□◯▱◃▹ "_sd}}),
        Value{"▹▱◯□ I ▙◉VE Shapes"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$trim", Document{{"input", "▹▱◯□ I ▙◉VE Shapes □◯▱◃"_sd}, {"chars", "□◯▱◃▹ "_sd}}),
        Value{"I ▙◉VE Shapes"_sd});
}

TEST(ExpressionTrimTest, DoesNotTrimFromMiddle) {
    // Using ascii whitespace.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", "  a\tb c  "_sd}}),
                    Value{"a\tb c"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "\n  a\nb  c \r\n "_sd}}),
        Value{"a\nb  c"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "  a\tb c  "_sd}}),
                    Value{"  a\tb c"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "\n  a\nb  c \r\n "_sd}}),
        Value{"\n  a\nb  c"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "  a\tb c  "_sd}}),
                    Value{"a\tb c  "_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$ltrim", Document{{"input", "\n  a\nb  c \r\n "_sd}}),
        Value{"a\nb  c \r\n "_sd});

    // Using unicode whitespace.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", "\u2001a\u2001\u000Ab\u2009c\u2004\u200A"_sd}}),
                    Value{"a\u2001\u000Ab\u2009c"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$ltrim", Document{{"input", "\u2001a\u2001\u000Ab\u2009c\u2004\u200A"_sd}}),
        Value{"a\u2001\u000Ab\u2009c\u2004\u200A"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$rtrim", Document{{"input", "\u2001a\u2001\u000Ab\u2009c\u2004\u200A"_sd}}),
        Value{"\u2001a\u2001\u000Ab\u2009c"_sd});

    // With custom ascii characters.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "xxXxXxx"_sd}, {"chars", "x"_sd}}),
        Value{"XxX"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "xxXxXxx"_sd}, {"chars", "x"_sd}}),
        Value{"xxXxX"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$ltrim", Document{{"input", "xxXxXxx"_sd}, {"chars", "x"_sd}}),
        Value{"XxXxx"_sd});

    // With custom unicode characters.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", "⌊y + 2⌋⌊x⌋"_sd}, {"chars", "⌊⌋"_sd}}),
                    Value{"y + 2⌋⌊x"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$ltrim", Document{{"input", "⌊y + 2⌋⌊x⌋"_sd}, {"chars", "⌊⌋"_sd}}),
                    Value{"y + 2⌋⌊x⌋"_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$rtrim", Document{{"input", "⌊y + 2⌋⌊x⌋"_sd}, {"chars", "⌊⌋"_sd}}),
                    Value{"⌊y + 2⌋⌊x"_sd});
}

TEST(ExpressionTrimTest, DoesTrimEntireString) {
    // Using ascii whitespace.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", "  \t \n  "_sd}}),
                    Value{""_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", "   \t  \n\0  "_sd}}),
                    Value{""_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$rtrim", Document{{"input", "  \t   "_sd}}),
                    Value{""_sd});

    // Using unicode whitespace.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$trim", Document{{"input", "\u2001 \u2001\t\u000A  \u2009\u2004\u200A"_sd}}),
        Value{""_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$ltrim", Document{{"input", "\u2001 \u2001\t\u000A  \u2009\u2004\u200A"_sd}}),
        Value{""_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$rtrim", Document{{"input", "\u2001 \u2001\t\u000A  \u2009\u2004\u200A"_sd}}),
        Value{""_sd});

    // With custom characters.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "xxXxXxx"_sd}, {"chars", "x"_sd}}),
        Value{"XxX"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$rtrim", Document{{"input", "xxXxXxx"_sd}, {"chars", "x"_sd}}),
        Value{"xxXxX"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$ltrim", Document{{"input", "xxXxXxx"_sd}, {"chars", "x"_sd}}),
        Value{"XxXxx"_sd});

    // With custom unicode characters.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "⌊y⌋⌊x⌋"_sd}, {"chars", "⌊xy⌋"_sd}}),
        Value{""_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$ltrim", Document{{"input", "⌊y⌋⌊x⌋"_sd}, {"chars", "⌊xy⌋"_sd}}),
                    Value{""_sd});
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$rtrim", Document{{"input", "⌊y⌋⌊x⌋"_sd}, {"chars", "⌊xy⌋"_sd}}),
                    Value{""_sd});
}

TEST(ExpressionTrimTest, DoesNotTrimAnyThingWithEmptyChars) {
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "abcde"_sd}, {"chars", ""_sd}}),
        Value{"abcde"_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", "  "_sd}, {"chars", ""_sd}}),
        Value{"  "_sd});
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", " ⌊y⌋⌊x⌋ "_sd}, {"chars", ""_sd}}),
        Value{" ⌊y⌋⌊x⌋ "_sd});
}

TEST(ExpressionTrimTest, TrimComparisonsShouldNotRespectCollation) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto caseInsensitive =
        stdx::make_unique<CollatorInterfaceMock>(CollatorInterfaceMock::MockType::kToLowerString);
    expCtx->setCollator(caseInsensitive.get());

    auto trim = Expression::parseExpression(expCtx,
                                            BSON("$trim" << BSON("input"
                                                                 << "xxXXxx"
                                                                 << "chars"
                                                                 << "x")),
                                            expCtx->variablesParseState);

    ASSERT_VALUE_EQ(trim->evaluate(Document()), Value("XX"_sd));
}

TEST(ExpressionTrimTest, ShouldRejectInvalidUTFInCharsArgument) {
    const auto twoThirdsOfExistsSymbol = "\xE2\x88"_sd;  // Full ∃ symbol would be "\xE2\x88\x83".
    ASSERT_THROWS(evaluateNamedArgExpression(
                      "$trim", Document{{"input", "abcde"_sd}, {"chars", twoThirdsOfExistsSymbol}}),
                  AssertionException);
    const auto stringWithExtraContinuationByte = "\xE2\x88\x83\x83"_sd;
    ASSERT_THROWS(
        evaluateNamedArgExpression(
            "$trim", Document{{"input", "ab∃"_sd}, {"chars", stringWithExtraContinuationByte}}),
        AssertionException);
    ASSERT_THROWS(
        evaluateNamedArgExpression("$ltrim",
                                   Document{{"input", "a" + twoThirdsOfExistsSymbol + "b∃"},
                                            {"chars", stringWithExtraContinuationByte}}),
        AssertionException);
}

TEST(ExpressionTrimTest, ShouldIgnoreUTF8InputWithTruncatedCodePoint) {
    const auto twoThirdsOfExistsSymbol = "\xE2\x88"_sd;  // Full ∃ symbol would be "\xE2\x88\x83".

    // We are OK producing invalid UTF-8 if the input string was invalid UTF-8, so if the truncated
    // code point is in the middle and we never examine it, it should work fine.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$rtrim",
            Document{{"input", "abc" + twoThirdsOfExistsSymbol + "edf∃"}, {"chars", "∃"_sd}}),
        Value("abc" + twoThirdsOfExistsSymbol + "edf"));

    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", twoThirdsOfExistsSymbol}, {"chars", "∃"_sd}}),
                    Value(twoThirdsOfExistsSymbol));
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$rtrim", Document{{"input", "abc" + twoThirdsOfExistsSymbol}, {"chars", "∃"_sd}}),
        Value("abc" + twoThirdsOfExistsSymbol));
}

TEST(ExpressionTrimTest, ShouldNotTrimUTF8InputWithTrailingExtraContinuationBytes) {
    const auto stringWithExtraContinuationByte = "\xE2\x88\x83\x83"_sd;

    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$trim",
            Document{{"input", stringWithExtraContinuationByte + "edf∃"}, {"chars", "∃"_sd}}),
        Value("\x83" + "edf"_sd));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim",
                        Document{{"input", "abc" + stringWithExtraContinuationByte + "edf∃"},
                                 {"chars", "∃"_sd}}),
                    Value("abc" + stringWithExtraContinuationByte + "edf"_sd));
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$trim",
            Document{{"input", "Abc" + stringWithExtraContinuationByte}, {"chars", "∃"_sd}}),
        Value("Abc" + stringWithExtraContinuationByte));
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression(
            "$rtrim", Document{{"input", stringWithExtraContinuationByte}, {"chars", "∃"_sd}}),
        Value(stringWithExtraContinuationByte));
}

TEST(ExpressionTrimTest, ShouldRetunNullIfInputIsNullish) {
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", BSONNULL}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", "$missingField"_sd}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$trim", Document{{"input", BSONUndefined}}),
                    Value(BSONNULL));

    // Test with a chars argument provided.
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", BSONNULL}, {"chars", "∃"_sd}}),
        Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", "$missingField"_sd}, {"chars", "∃"_sd}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", BSONUndefined}, {"chars", "∃"_sd}}),
        Value(BSONNULL));

    // Test other variants of trim.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression("$ltrim", Document{{"input", BSONNULL}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$rtrim", Document{{"input", "$missingField"_sd}, {"chars", "∃"_sd}}),
                    Value(BSONNULL));
}

TEST(ExpressionTrimTest, ShouldRetunNullIfCharsIsNullish) {
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", " x "_sd}, {"chars", BSONNULL}}),
        Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", " x "_sd}, {"chars", "$missingField"_sd}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", " x "_sd}, {"chars", BSONUndefined}}),
                    Value(BSONNULL));

    // Test other variants of trim.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$ltrim", Document{{"input", " x "_sd}, {"chars", "$missingField"_sd}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$rtrim", Document{{"input", " x "_sd}, {"chars", BSONUndefined}}),
                    Value(BSONNULL));
}

TEST(ExpressionTrimTest, ShouldReturnNullIfBothCharsAndCharsAreNullish) {
    ASSERT_VALUE_EQ(
        evaluateNamedArgExpression("$trim", Document{{"input", BSONNULL}, {"chars", BSONNULL}}),
        Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", BSONUndefined}, {"chars", "$missingField"_sd}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$trim", Document{{"input", "$missingField"_sd}, {"chars", BSONUndefined}}),
                    Value(BSONNULL));

    // Test other variants of trim.
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$rtrim", Document{{"input", BSONNULL}, {"chars", "$missingField"_sd}}),
                    Value(BSONNULL));
    ASSERT_VALUE_EQ(evaluateNamedArgExpression(
                        "$ltrim", Document{{"input", "$missingField"_sd}, {"chars", BSONNULL}}),
                    Value(BSONNULL));
}

TEST(ExpressionTrimTest, DoesOptimizeToConstantWithNoChars) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto trim = Expression::parseExpression(expCtx,
                                            BSON("$trim" << BSON("input"
                                                                 << " abc ")),
                                            expCtx->variablesParseState);
    auto optimized = trim->optimize();
    auto constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_TRUE(constant);
    ASSERT_VALUE_EQ(constant->getValue(), Value("abc"_sd));

    // Test that it optimizes to a constant if the input also optimizes to a constant.
    trim = Expression::parseExpression(
        expCtx,
        BSON("$trim" << BSON("input" << BSON("$concat" << BSON_ARRAY(" "
                                                                     << "abc ")))),
        expCtx->variablesParseState);
    optimized = trim->optimize();
    constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_TRUE(constant);
    ASSERT_VALUE_EQ(constant->getValue(), Value("abc"_sd));
}

TEST(ExpressionTrimTest, DoesOptimizeToConstantWithCustomChars) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto trim = Expression::parseExpression(expCtx,
                                            BSON("$trim" << BSON("input"
                                                                 << " abc "
                                                                 << "chars"
                                                                 << " ")),
                                            expCtx->variablesParseState);
    auto optimized = trim->optimize();
    auto constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_TRUE(constant);
    ASSERT_VALUE_EQ(constant->getValue(), Value("abc"_sd));

    // Test that it optimizes to a constant if the chars argument optimizes to a constant.
    trim = Expression::parseExpression(
        expCtx,
        BSON("$trim" << BSON("input"
                             << "  abc "
                             << "chars"
                             << BSON("$substrCP" << BSON_ARRAY("  " << 1 << 1)))),
        expCtx->variablesParseState);
    optimized = trim->optimize();
    constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_TRUE(constant);
    ASSERT_VALUE_EQ(constant->getValue(), Value("abc"_sd));

    // Test that it optimizes to a constant if both arguments optimize to a constant.
    trim = Expression::parseExpression(
        expCtx,
        BSON("$trim" << BSON("input" << BSON("$concat" << BSON_ARRAY(" "
                                                                     << "abc "))
                                     << "chars"
                                     << BSON("$substrCP" << BSON_ARRAY("  " << 1 << 1)))),
        expCtx->variablesParseState);
    optimized = trim->optimize();
    constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_TRUE(constant);
    ASSERT_VALUE_EQ(constant->getValue(), Value("abc"_sd));
}

TEST(ExpressionTrimTest, DoesNotOptimizeToConstantWithFieldPaths) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    // 'input' is field path.
    auto trim = Expression::parseExpression(expCtx,
                                            BSON("$trim" << BSON("input"
                                                                 << "$inputField")),
                                            expCtx->variablesParseState);
    auto optimized = trim->optimize();
    auto constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_FALSE(constant);

    // 'chars' is field path.
    trim = Expression::parseExpression(expCtx,
                                       BSON("$trim" << BSON("input"
                                                            << " abc "
                                                            << "chars"
                                                            << "$secondInput")),
                                       expCtx->variablesParseState);
    optimized = trim->optimize();
    constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_FALSE(constant);

    // Both are field paths.
    trim = Expression::parseExpression(expCtx,
                                       BSON("$trim" << BSON("input"
                                                            << "$inputField"
                                                            << "chars"
                                                            << "$secondInput")),
                                       expCtx->variablesParseState);
    optimized = trim->optimize();
    constant = dynamic_cast<ExpressionConstant*>(optimized.get());
    ASSERT_FALSE(constant);
}

TEST(ExpressionTrimTest, DoesAddInputDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    auto trim = Expression::parseExpression(expCtx,
                                            BSON("$trim" << BSON("input"
                                                                 << "$inputField")),
                                            expCtx->variablesParseState);
    DepsTracker deps;
    trim->addDependencies(&deps);
    ASSERT_EQ(deps.fields.count("inputField"), 1u);
    ASSERT_EQ(deps.fields.size(), 1u);
}

TEST(ExpressionTrimTest, DoesAddCharsDependencies) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    auto trim = Expression::parseExpression(expCtx,
                                            BSON("$trim" << BSON("input"
                                                                 << "$inputField"
                                                                 << "chars"
                                                                 << "$$CURRENT.a")),
                                            expCtx->variablesParseState);
    DepsTracker deps;
    trim->addDependencies(&deps);
    ASSERT_EQ(deps.fields.count("inputField"), 1u);
    ASSERT_EQ(deps.fields.count("a"), 1u);
    ASSERT_EQ(deps.fields.size(), 2u);
}

TEST(ExpressionTrimTest, DoesSerializeCorrectly) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    auto trim = Expression::parseExpression(expCtx,
                                            BSON("$trim" << BSON("input"
                                                                 << " abc ")),
                                            expCtx->variablesParseState);
    ASSERT_VALUE_EQ(trim->serialize(false), trim->serialize(true));
    ASSERT_VALUE_EQ(
        trim->serialize(false),
        Value(Document{{"$trim", Document{{"input", Document{{"$const", " abc "_sd}}}}}}));

    // Make sure we can re-parse it and evaluate it.
    auto reparsedTrim = Expression::parseExpression(
        expCtx, trim->serialize(false).getDocument().toBson(), expCtx->variablesParseState);
    ASSERT_VALUE_EQ(reparsedTrim->evaluate(Document()), Value("abc"_sd));

    // Use $ltrim, and specify the 'chars' option.
    trim = Expression::parseExpression(expCtx,
                                       BSON("$ltrim" << BSON("input"
                                                             << "$inputField"
                                                             << "chars"
                                                             << "$$CURRENT.a")),
                                       expCtx->variablesParseState);
    ASSERT_VALUE_EQ(
        trim->serialize(false),
        Value(Document{{"$ltrim", Document{{"input", "$inputField"_sd}, {"chars", "$a"_sd}}}}));

    // Make sure we can re-parse it and evaluate it.
    reparsedTrim = Expression::parseExpression(
        expCtx, trim->serialize(false).getDocument().toBson(), expCtx->variablesParseState);
    ASSERT_VALUE_EQ(reparsedTrim->evaluate(Document{{"inputField", " , 4"_sd}, {"a", " ,"_sd}}),
                    Value("4"_sd));
}
}  // namespace Trim

namespace Type {

TEST(ExpressionTypeTest, WithMinKeyValue) {
    assertExpectedResults("$type", {{{Value(MINKEY)}, Value("minKey"_sd)}});
}

TEST(ExpressionTypeTest, WithDoubleValue) {
    assertExpectedResults("$type", {{{Value(1.0)}, Value("double"_sd)}});
}

TEST(ExpressionTypeTest, WithStringValue) {
    assertExpectedResults("$type", {{{Value("stringValue"_sd)}, Value("string"_sd)}});
}

TEST(ExpressionTypeTest, WithObjectValue) {
    BSONObj objectVal = fromjson("{a: {$literal: 1}}");
    assertExpectedResults("$type", {{{Value(objectVal)}, Value("object"_sd)}});
}

TEST(ExpressionTypeTest, WithArrayValue) {
    assertExpectedResults("$type", {{{Value(BSON_ARRAY(1 << 2))}, Value("array"_sd)}});
}

TEST(ExpressionTypeTest, WithBinDataValue) {
    BSONBinData binDataVal = BSONBinData("", 0, BinDataGeneral);
    assertExpectedResults("$type", {{{Value(binDataVal)}, Value("binData"_sd)}});
}

TEST(ExpressionTypeTest, WithUndefinedValue) {
    assertExpectedResults("$type", {{{Value(BSONUndefined)}, Value("undefined"_sd)}});
}

TEST(ExpressionTypeTest, WithOIDValue) {
    assertExpectedResults("$type", {{{Value(OID())}, Value("objectId"_sd)}});
}

TEST(ExpressionTypeTest, WithBoolValue) {
    assertExpectedResults("$type", {{{Value(true)}, Value("bool"_sd)}});
}

TEST(ExpressionTypeTest, WithDateValue) {
    Date_t dateVal = BSON("" << DATENOW).firstElement().Date();
    assertExpectedResults("$type", {{{Value(dateVal)}, Value("date"_sd)}});
}

TEST(ExpressionTypeTest, WithNullValue) {
    assertExpectedResults("$type", {{{Value(BSONNULL)}, Value("null"_sd)}});
}

TEST(ExpressionTypeTest, WithRegexValue) {
    assertExpectedResults("$type", {{{Value(BSONRegEx("a.b"))}, Value("regex"_sd)}});
}

TEST(ExpressionTypeTest, WithSymbolValue) {
    assertExpectedResults("$type", {{{Value(BSONSymbol("a"))}, Value("symbol"_sd)}});
}

TEST(ExpressionTypeTest, WithDBRefValue) {
    assertExpectedResults("$type", {{{Value(BSONDBRef("", OID()))}, Value("dbPointer"_sd)}});
}

TEST(ExpressionTypeTest, WithCodeWScopeValue) {
    assertExpectedResults(
        "$type",
        {{{Value(BSONCodeWScope("var x = 3", BSONObj()))}, Value("javascriptWithScope"_sd)}});
}

TEST(ExpressionTypeTest, WithCodeValue) {
    assertExpectedResults("$type", {{{Value(BSONCode("var x = 3"))}, Value("javascript"_sd)}});
}

TEST(ExpressionTypeTest, WithIntValue) {
    assertExpectedResults("$type", {{{Value(1)}, Value("int"_sd)}});
}

TEST(ExpressionTypeTest, WithDecimalValue) {
    assertExpectedResults("$type", {{{Value(Decimal128(0.3))}, Value("decimal"_sd)}});
}

TEST(ExpressionTypeTest, WithLongValue) {
    assertExpectedResults("$type", {{{Value(1LL)}, Value("long"_sd)}});
}

TEST(ExpressionTypeTest, WithTimestampValue) {
    assertExpectedResults("$type", {{{Value(Timestamp(0, 0))}, Value("timestamp"_sd)}});
}

TEST(ExpressionTypeTest, WithMaxKeyValue) {
    assertExpectedResults("$type", {{{Value(MAXKEY)}, Value("maxKey"_sd)}});
}

}  // namespace Type

namespace BuiltinRemoveVariable {

TEST(BuiltinRemoveVariableTest, TypeOfRemoveIsMissing) {
    assertExpectedResults("$type", {{{Value("$$REMOVE"_sd)}, Value("missing"_sd)}});
}

TEST(BuiltinRemoveVariableTest, LiteralEscapesRemoveVar) {
    assertExpectedResults(
        "$literal", {{{Value("$$REMOVE"_sd)}, Value(std::vector<Value>{Value("$$REMOVE"_sd)})}});
}

TEST(BuiltinRemoveVariableTest, RemoveSerializesCorrectly) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto expression = ExpressionFieldPath::parse(expCtx, "$$REMOVE", vps);
    ASSERT_BSONOBJ_EQ(BSON("foo"
                           << "$$REMOVE"),
                      BSON("foo" << expression->serialize(false)));
}

TEST(BuiltinRemoveVariableTest, RemoveSerializesCorrectlyWithTrailingPath) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto expression = ExpressionFieldPath::parse(expCtx, "$$REMOVE.a.b", vps);
    ASSERT_BSONOBJ_EQ(BSON("foo"
                           << "$$REMOVE.a.b"),
                      BSON("foo" << expression->serialize(false)));
}

TEST(BuiltinRemoveVariableTest, RemoveSerializesCorrectlyAfterOptimization) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    auto expression = ExpressionFieldPath::parse(expCtx, "$$REMOVE.a.b", vps);
    auto optimizedExpression = expression->optimize();
    ASSERT(dynamic_cast<ExpressionConstant*>(optimizedExpression.get()));
    ASSERT_BSONOBJ_EQ(BSON("foo"
                           << "$$REMOVE"),
                      BSON("foo" << optimizedExpression->serialize(false)));
}

}  // namespace BuiltinRemoveVariable

/* ------------------------- ExpressionMergeObjects -------------------------- */

namespace ExpressionMergeObjects {

TEST(ExpressionMergeObjects, MergingWithSingleObjectShouldLeaveUnchanged) {
    assertExpectedResults("$mergeObjects", {{{}, {Document({})}}});

    auto doc = Document({{"a", 1}, {"b", 1}});
    assertExpectedResults("$mergeObjects", {{{doc}, doc}});
}

TEST(ExpressionMergeObjects, MergingDisjointObjectsShouldIncludeAllFields) {
    auto first = Document({{"a", 1}, {"b", 1}});
    auto second = Document({{"c", 1}});
    assertExpectedResults("$mergeObjects",
                          {{{first, second}, Document({{"a", 1}, {"b", 1}, {"c", 1}})}});
}

TEST(ExpressionMergeObjects, MergingIntersectingObjectsShouldOverrideInOrderReceived) {
    auto first = Document({{"a", "oldValue"_sd}, {"b", 0}, {"c", 1}});
    auto second = Document({{"a", "newValue"_sd}});
    assertExpectedResults(
        "$mergeObjects", {{{first, second}, Document({{"a", "newValue"_sd}, {"b", 0}, {"c", 1}})}});
}

TEST(ExpressionMergeObjects, MergingIntersectingEmbeddedObjectsShouldOverrideInOrderReceived) {
    auto firstSubDoc = Document({{"a", 1}, {"b", 2}, {"c", 3}});
    auto secondSubDoc = Document({{"a", 2}, {"b", 1}});
    auto first = Document({{"d", 1}, {"subDoc", firstSubDoc}});
    auto second = Document({{"subDoc", secondSubDoc}});
    auto expected = Document({{"d", 1}, {"subDoc", secondSubDoc}});
    assertExpectedResults("$mergeObjects", {{{first, second}, expected}});
}

TEST(ExpressionMergeObjects, MergingWithEmptyDocumentShouldIgnore) {
    auto first = Document({{"a", 0}, {"b", 1}, {"c", 1}});
    auto second = Document({});
    auto expected = Document({{"a", 0}, {"b", 1}, {"c", 1}});
    assertExpectedResults("$mergeObjects", {{{first, second}, expected}});
}

TEST(ExpressionMergeObjects, MergingSingleArgumentArrayShouldUnwindAndMerge) {
    std::vector<Document> first = {Document({{"a", 1}}), Document({{"a", 2}})};
    auto expected = Document({{"a", 2}});
    assertExpectedResults("$mergeObjects", {{{first}, expected}});
}

TEST(ExpressionMergeObjects, MergingArrayWithDocumentShouldThrowException) {
    std::vector<Document> first = {Document({{"a", 1}}), Document({{"a", 2}})};
    auto second = Document({{"b", 2}});
    ASSERT_THROWS_CODE(
        evaluateExpression("$mergeObjects", {first, second}), AssertionException, 40400);
}

TEST(ExpressionMergeObjects, MergingArrayContainingInvalidTypesShouldThrowException) {
    std::vector<Value> first = {Value(Document({{"validType", 1}})), Value("invalidType"_sd)};
    ASSERT_THROWS_CODE(evaluateExpression("$mergeObjects", {first}), AssertionException, 40400);
}

TEST(ExpressionMergeObjects, MergingNonObjectsShouldThrowException) {
    ASSERT_THROWS_CODE(
        evaluateExpression("$mergeObjects", {"invalidArg"_sd}), AssertionException, 40400);

    ASSERT_THROWS_CODE(
        evaluateExpression("$mergeObjects", {"invalidArg"_sd, Document({{"validArg", 1}})}),
        AssertionException,
        40400);

    ASSERT_THROWS_CODE(evaluateExpression("$mergeObjects", {1, Document({{"validArg", 1}})}),
                       AssertionException,
                       40400);
}

}  // namespace ExpressionMergeObjects


namespace ToLower {

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObj = BSON("" << spec());
        BSONElement specElement = specObj.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult()), toBson(expression->evaluate(Document())));
    }

protected:
    virtual string str() = 0;
    virtual string expectedResult() = 0;

private:
    BSONObj spec() {
        return BSON("$toLower" << BSON_ARRAY(str()));
    }
};

/** String beginning with a null character. */
class NullBegin : public ExpectedResultBase {
    string str() {
        return string("\0aB", 3);
    }
    string expectedResult() {
        return string("\0ab", 3);
    }
};

/** String containing a null character. */
class NullMiddle : public ExpectedResultBase {
    string str() {
        return string("a\0B", 3);
    }
    string expectedResult() {
        return string("a\0b", 3);
    }
};

/** String ending with a null character. */
class NullEnd : public ExpectedResultBase {
    string str() {
        return string("aB\0", 3);
    }
    string expectedResult() {
        return string("ab\0", 3);
    }
};

}  // namespace ToLower

namespace ToUpper {

class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        BSONObj specObj = BSON("" << spec());
        BSONElement specElement = specObj.firstElement();
        VariablesParseState vps = expCtx->variablesParseState;
        intrusive_ptr<Expression> expression = Expression::parseOperand(expCtx, specElement, vps);
        ASSERT_BSONOBJ_EQ(constify(spec()), expressionToBson(expression));
        ASSERT_BSONOBJ_EQ(BSON("" << expectedResult()), toBson(expression->evaluate(Document())));
    }

protected:
    virtual string str() = 0;
    virtual string expectedResult() = 0;

private:
    BSONObj spec() {
        return BSON("$toUpper" << BSON_ARRAY(str()));
    }
};

/** String beginning with a null character. */
class NullBegin : public ExpectedResultBase {
    string str() {
        return string("\0aB", 3);
    }
    string expectedResult() {
        return string("\0AB", 3);
    }
};

/** String containing a null character. */
class NullMiddle : public ExpectedResultBase {
    string str() {
        return string("a\0B", 3);
    }
    string expectedResult() {
        return string("A\0B", 3);
    }
};

/** String ending with a null character. */
class NullEnd : public ExpectedResultBase {
    string str() {
        return string("aB\0", 3);
    }
    string expectedResult() {
        return string("AB\0", 3);
    }
};

}  // namespace ToUpper

namespace AllAnyElements {
class ExpectedResultBase {
public:
    virtual ~ExpectedResultBase() {}
    void run() {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        const Document spec = getSpec();
        const Value args = spec["input"];
        if (!spec["expected"].missing()) {
            FieldIterator fields(spec["expected"].getDocument());
            while (fields.more()) {
                const Document::FieldPair field(fields.next());
                const Value expected = field.second;
                const BSONObj obj = BSON(field.first << args);
                VariablesParseState vps = expCtx->variablesParseState;
                const intrusive_ptr<Expression> expr =
                    Expression::parseExpression(expCtx, obj, vps);
                const Value result = expr->evaluate(Document());
                if (ValueComparator().evaluate(result != expected)) {
                    string errMsg = str::stream()
                        << "for expression " << field.first.toString() << " with argument "
                        << args.toString() << " full tree: " << expr->serialize(false).toString()
                        << " expected: " << expected.toString()
                        << " but got: " << result.toString();
                    FAIL(errMsg);
                }
                // TODO test optimize here
            }
        }
        if (!spec["error"].missing()) {
            const vector<Value>& asserters = spec["error"].getArray();
            size_t n = asserters.size();
            for (size_t i = 0; i < n; i++) {
                const BSONObj obj = BSON(asserters[i].getString() << args);
                VariablesParseState vps = expCtx->variablesParseState;
                ASSERT_THROWS(
                    [&] {
                        // NOTE: parse and evaluatation failures are treated the
                        // same
                        const intrusive_ptr<Expression> expr =
                            Expression::parseExpression(expCtx, obj, vps);
                        expr->evaluate(Document());
                    }(),
                    AssertionException);
            }
        }
    }

private:
    virtual Document getSpec() = 0;
};

class JustFalse : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(false)) << "expected"
                           << DOC("$allElementsTrue" << false << "$anyElementTrue" << false));
    }
};

class JustTrue : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(true)) << "expected"
                           << DOC("$allElementsTrue" << true << "$anyElementTrue" << true));
    }
};

class OneTrueOneFalse : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(true << false)) << "expected"
                           << DOC("$allElementsTrue" << false << "$anyElementTrue" << true));
    }
};

class Empty : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(vector<Value>()) << "expected"
                           << DOC("$allElementsTrue" << true << "$anyElementTrue" << false));
    }
};

class TrueViaInt : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(1)) << "expected"
                           << DOC("$allElementsTrue" << true << "$anyElementTrue" << true));
    }
};

class FalseViaInt : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(DOC_ARRAY(0)) << "expected"
                           << DOC("$allElementsTrue" << false << "$anyElementTrue" << false));
    }
};

class Null : public ExpectedResultBase {
    Document getSpec() {
        return DOC("input" << DOC_ARRAY(BSONNULL) << "error" << DOC_ARRAY("$allElementsTrue"_sd
                                                                          << "$anyElementTrue"_sd));
    }
};

}  // namespace AllAnyElements

namespace GetComputedPathsTest {

TEST(GetComputedPathsTest, ExpressionFieldPathDoesNotCountAsRenameWhenUsingRemoveBuiltin) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto expr = ExpressionFieldPath::parse(expCtx, "$$REMOVE", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("a", Variables::kRootId);
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("a"), 1u);
    ASSERT(computedPaths.renames.empty());
}

TEST(GetComputedPathsTest, ExpressionFieldPathDoesNotCountAsRenameWhenOnlyRoot) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto expr = ExpressionFieldPath::parse(expCtx, "$$ROOT", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("a", Variables::kRootId);
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("a"), 1u);
    ASSERT(computedPaths.renames.empty());
}

TEST(GetComputedPathsTest, ExpressionFieldPathDoesNotCountAsRenameWithNonMatchingUserVariable) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    expCtx->variablesParseState.defineVariable("userVar");
    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar.b", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("a", Variables::kRootId);
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("a"), 1u);
    ASSERT(computedPaths.renames.empty());
}

TEST(GetComputedPathsTest, ExpressionFieldPathDoesNotCountAsRenameWhenDotted) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto expr = ExpressionFieldPath::parse(expCtx, "$a.b", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("c", Variables::kRootId);
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("c"), 1u);
    ASSERT(computedPaths.renames.empty());
}

TEST(GetComputedPathsTest, ExpressionFieldPathDoesCountAsRename) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto expr = ExpressionFieldPath::parse(expCtx, "$a", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("b", Variables::kRootId);
    ASSERT(computedPaths.paths.empty());
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["b"], "a");
}

TEST(GetComputedPathsTest, ExpressionFieldPathDoesCountAsRenameWithExplicitRoot) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto expr = ExpressionFieldPath::parse(expCtx, "$$ROOT.a", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("b", Variables::kRootId);
    ASSERT(computedPaths.paths.empty());
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["b"], "a");
}

TEST(GetComputedPathsTest, ExpressionFieldPathDoesCountAsRenameWithExplicitCurrent) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto expr = ExpressionFieldPath::parse(expCtx, "$$CURRENT.a", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("b", Variables::kRootId);
    ASSERT(computedPaths.paths.empty());
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["b"], "a");
}

TEST(GetComputedPathsTest, ExpressionFieldPathDoesCountAsRenameWithMatchingUserVariable) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto varId = expCtx->variablesParseState.defineVariable("userVar");
    auto expr = ExpressionFieldPath::parse(expCtx, "$$userVar.a", expCtx->variablesParseState);
    auto computedPaths = expr->getComputedPaths("b", varId);
    ASSERT(computedPaths.paths.empty());
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["b"], "a");
}

TEST(GetComputedPathsTest, ExpressionObjectCorrectlyReportsComputedPaths) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject = fromjson("{a: '$b', c: {$add: [1, 3]}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionObject*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("d");
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("d.c"), 1u);
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["d.a"], "b");
}

TEST(GetComputedPathsTest, ExpressionObjectCorrectlyReportsComputedPathsNested) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject = fromjson(
        "{a: {b: '$c'},"
        "d: {$map: {input: '$e', as: 'iter', in: {f: '$$iter.g'}}}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionObject*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("h");
    ASSERT(computedPaths.paths.empty());
    ASSERT_EQ(computedPaths.renames.size(), 2u);
    ASSERT_EQ(computedPaths.renames["h.a.b"], "c");
    ASSERT_EQ(computedPaths.renames["h.d.f"], "e.g");
}

TEST(GetComputedPathsTest, ExpressionMapCorrectlyReportsComputedPaths) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject =
        fromjson("{$map: {input: '$a', as: 'iter', in: {b: '$$iter.c', d: {$add: [1, 2]}}}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionMap*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("e");
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("e.d"), 1u);
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["e.b"], "a.c");
}

TEST(GetComputedPathsTest, ExpressionMapCorrectlyReportsComputedPathsWithDefaultVarName) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject = fromjson("{$map: {input: '$a', in: {b: '$$this.c', d: {$add: [1, 2]}}}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionMap*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("e");
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("e.d"), 1u);
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["e.b"], "a.c");
}

TEST(GetComputedPathsTest, ExpressionMapCorrectlyReportsComputedPathsWithNestedExprObject) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject = fromjson("{$map: {input: '$a', in: {b: {c: '$$this.d'}}}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionMap*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("e");
    ASSERT(computedPaths.paths.empty());
    ASSERT_EQ(computedPaths.renames.size(), 1u);
    ASSERT_EQ(computedPaths.renames["e.b.c"], "a.d");
}

TEST(GetComputedPathsTest, ExpressionMapNotConsideredRenameWithWrongRootVariable) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject = fromjson("{$map: {input: '$a', as: 'iter', in: {b: '$c'}}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionMap*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("d");
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("d"), 1u);
    ASSERT(computedPaths.renames.empty());
}

TEST(GetComputedPathsTest, ExpressionMapNotConsideredRenameWithWrongVariableNoExpressionObject) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject = fromjson("{$map: {input: '$a', as: 'iter', in: '$b'}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionMap*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("d");
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("d"), 1u);
    ASSERT(computedPaths.renames.empty());
}

TEST(GetComputedPathsTest, ExpressionMapNotConsideredRenameWithDottedInputPath) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    auto specObject = fromjson("{$map: {input: '$a.b', as: 'iter', in: {c: '$$iter.d'}}}}");
    auto expr = Expression::parseObject(expCtx, specObject, expCtx->variablesParseState);
    ASSERT(dynamic_cast<ExpressionMap*>(expr.get()));
    auto computedPaths = expr->getComputedPaths("e");
    ASSERT_EQ(computedPaths.paths.size(), 1u);
    ASSERT_EQ(computedPaths.paths.count("e"), 1u);
    ASSERT(computedPaths.renames.empty());
}

}  // namespace GetComputedPathsTest

namespace expression_meta_test {
TEST(ExpressionMetaTest, ExpressionMetaSearchScore) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    BSONObj expr = fromjson("{$meta: \"searchScore\"}");
    auto expressionMeta = ExpressionMeta::parse(expCtx, expr.firstElement(), vps);

    MutableDocument doc;
    doc.setSearchScore(1.234);
    Value val = expressionMeta->evaluate(doc.freeze());
    ASSERT_EQ(val.getDouble(), 1.234);
}

TEST(ExpressionMetaTest, ExpressionMetaSearchHighlights) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
    VariablesParseState vps = expCtx->variablesParseState;
    BSONObj expr = fromjson("{$meta: \"searchHighlights\"}");
    auto expressionMeta = ExpressionMeta::parse(expCtx, expr.firstElement(), vps);

    MutableDocument doc;
    Document highlights = DOC("this part" << 1 << "is opaque to the server" << 1);
    doc.setSearchHighlights(Value(highlights));

    Value val = expressionMeta->evaluate(doc.freeze());
    ASSERT_DOCUMENT_EQ(val.getDocument(), highlights);
}
}  // namespace expression_meta_test

namespace ExpressionRegexTest {

class ExpressionRegexTest {
public:
    template <typename ExpressionRegexSubClass>
    static intrusive_ptr<Expression> generateOptimizedExpression(const BSONObj& input) {
        intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());
        auto expression = ExpressionRegexSubClass::parse(
            expCtx, input.firstElement(), expCtx->variablesParseState);
        return expression->optimize();
    }

    static void testAllExpressions(const BSONObj& input,
                                   bool optimized,
                                   const std::vector<Value>& expectedFindAllOutput) {
        {
            // For $regexFindAll.
            auto expression = generateOptimizedExpression<ExpressionRegexFindAll>(input);
            auto regexFindAllExpr = dynamic_cast<ExpressionRegexFindAll*>(expression.get());
            ASSERT_EQ(regexFindAllExpr->hasConstantRegex(), optimized);
            Value output = regexFindAllExpr->evaluate(Document());
            ASSERT_VALUE_EQ(output, Value(expectedFindAllOutput));
        }

        {
            // For $regexFind.
            auto expression = generateOptimizedExpression<ExpressionRegexFind>(input);
            auto regexFindExpr = dynamic_cast<ExpressionRegexFind*>(expression.get());
            ASSERT_EQ(regexFindExpr->hasConstantRegex(), optimized);
            Value output = regexFindExpr->evaluate(Document());
            ASSERT_VALUE_EQ(
                output, expectedFindAllOutput.empty() ? Value(BSONNULL) : expectedFindAllOutput[0]);
        }

        {
            // For $regexMatch.
            auto expression = generateOptimizedExpression<ExpressionRegexMatch>(input);
            auto regexMatchExpr = dynamic_cast<ExpressionRegexMatch*>(expression.get());
            ASSERT_EQ(regexMatchExpr->hasConstantRegex(), optimized);
            Value output = regexMatchExpr->evaluate(Document());
            ASSERT_VALUE_EQ(output, expectedFindAllOutput.empty() ? Value(false) : Value(true));
        }
    }
};

TEST(ExpressionRegexTest, BasicTest) {
    ExpressionRegexTest::testAllExpressions(
        fromjson("{$regexFindAll : {input: 'asdf', regex: '^as' }}"),
        true,
        {Value(fromjson("{match: 'as', idx:0, captures:[]}"))});
}

TEST(ExpressionRegexTest, ExtendedRegexOptions) {
    ExpressionRegexTest::testAllExpressions(
        fromjson("{$regexFindAll : {input: 'FirstLine\\nSecondLine', regex: "
                 "'^second' , options: 'mi'}}"),
        true,
        {Value(fromjson("{match: 'Second', idx:10, captures:[]}"))});
}

TEST(ExpressionRegexTest, MultipleMatches) {
    ExpressionRegexTest::testAllExpressions(
        fromjson("{$regexFindAll : {input: 'a1b2c3', regex: '([a-c][1-3])' }}"),
        true,
        {Value(fromjson("{match: 'a1', idx:0, captures:['a1']}")),
         Value(fromjson("{match: 'b2', idx:2, captures:['b2']}")),
         Value(fromjson("{match: 'c3', idx:4, captures:['c3']}"))});
}

TEST(ExpressionRegexTest, OptimizPatternWhenInputIsVariable) {
    ExpressionRegexTest::testAllExpressions(
        fromjson("{$regexFindAll : {input: '$input', regex: '([a-c][1-3])' }}"), true, {});
}

TEST(ExpressionRegexTest, NoOptimizePatternWhenRegexVariable) {
    ExpressionRegexTest::testAllExpressions(
        fromjson("{$regexFindAll : {input: 'asdf', regex: '$regex' }}"), false, {});
}

TEST(ExpressionRegexTest, NoOptimizePatternWhenOptionsVariable) {
    ExpressionRegexTest::testAllExpressions(
        fromjson("{$regexFindAll : {input: 'asdf', regex: '(asdf)', options: '$options' }}"),
        false,
        {Value(fromjson("{match: 'asdf', idx:0, captures:['asdf']}"))});
}

TEST(ExpressionRegexTest, NoMatch) {
    ExpressionRegexTest::testAllExpressions(
        fromjson("{$regexFindAll : {input: 'a1b2c3', regex: 'ab' }}"), true, {});
}

TEST(ExpressionRegexTest, FailureCaseBadRegexType) {
    ASSERT_THROWS_CODE(ExpressionRegexTest::testAllExpressions(
                           fromjson("{$regexFindAll : {input: 'FirstLine\\nSecondLine', regex: "
                                    "{invalid : 'regex'} , options: 'mi'}}"),
                           false,
                           {}),
                       AssertionException,
                       51105);
}

TEST(ExpressionRegexTest, FailureCaseBadRegexPattern) {
    ASSERT_THROWS_CODE(
        ExpressionRegexTest::testAllExpressions(
            fromjson("{$regexFindAll : {input: 'FirstLine\\nSecondLine', regex: '[0-9'}}"),
            false,
            {}),
        AssertionException,
        51111);
}

TEST(ExpressionRegexTest, InvalidUTF8InInput) {
    std::string inputField = "1234 ";
    // Append an invalid UTF-8 character.
    inputField += '\xe5';
    inputField += "  1234";
    BSONObj input(fromjson("{$regexFindAll: {input: '" + inputField + "', regex: '[0-9]'}}"));

    // Verify that PCRE will error during execution if input is not a valid UTF-8.
    ASSERT_THROWS_CODE(
        ExpressionRegexTest::testAllExpressions(input, true, {}), AssertionException, 51156);
}

TEST(ExpressionRegexTest, InvalidUTF8InRegex) {
    std::string regexField = "1234 ";
    // Append an invalid UTF-8 character.
    regexField += '\xe5';
    BSONObj input(fromjson("{$regexFindAll: {input: '123456', regex: '" + regexField + "'}}"));
    // Verify that PCRE will error if REGEX is not a valid UTF-8.
    ASSERT_THROWS_CODE(
        ExpressionRegexTest::testAllExpressions(input, false, {}), AssertionException, 51111);
}

}  // namespace ExpressionRegexTest

class All : public Suite {
public:
    All() : Suite("expression") {}
    void setupTests() {
        add<Add::NullDocument>();
        add<Add::NoOperands>();
        add<Add::Date>();
        add<Add::String>();
        add<Add::Bool>();
        add<Add::Int>();
        add<Add::Long>();
        add<Add::Double>();
        add<Add::Null>();
        add<Add::Undefined>();
        add<Add::IntInt>();
        add<Add::IntIntNoOverflow>();
        add<Add::IntLong>();
        add<Add::IntLongOverflowToDouble>();
        add<Add::IntDouble>();
        add<Add::IntDate>();
        add<Add::LongDouble>();
        add<Add::LongDoubleNoOverflow>();
        add<Add::IntNull>();
        add<Add::LongUndefined>();

        add<And::NoOperands>();
        add<And::True>();
        add<And::False>();
        add<And::TrueTrue>();
        add<And::TrueFalse>();
        add<And::FalseTrue>();
        add<And::FalseFalse>();
        add<And::TrueTrueTrue>();
        add<And::TrueTrueFalse>();
        add<And::TrueTrueFalse>();
        add<And::ZeroOne>();
        add<And::OneTwo>();
        add<And::FieldPath>();
        add<And::OptimizeConstantExpression>();
        add<And::NonConstant>();
        add<And::ConstantNonConstantTrue>();
        add<And::ConstantNonConstantFalse>();
        add<And::NonConstantOne>();
        add<And::NonConstantZero>();
        add<And::NonConstantNonConstantOne>();
        add<And::NonConstantNonConstantZero>();
        add<And::ZeroOneNonConstant>();
        add<And::OneOneNonConstant>();
        add<And::Nested>();
        add<And::NestedZero>();

        add<CoerceToBool::EvaluateTrue>();
        add<CoerceToBool::EvaluateFalse>();
        add<CoerceToBool::Dependencies>();
        add<CoerceToBool::AddToBsonObj>();
        add<CoerceToBool::AddToBsonArray>();

        add<Compare::EqLt>();
        add<Compare::EqEq>();
        add<Compare::EqGt>();
        add<Compare::NeLt>();
        add<Compare::NeEq>();
        add<Compare::NeGt>();
        add<Compare::GtLt>();
        add<Compare::GtEq>();
        add<Compare::GtGt>();
        add<Compare::GteLt>();
        add<Compare::GteEq>();
        add<Compare::GteGt>();
        add<Compare::LtLt>();
        add<Compare::LtEq>();
        add<Compare::LtGt>();
        add<Compare::LteLt>();
        add<Compare::LteEq>();
        add<Compare::LteGt>();
        add<Compare::CmpLt>();
        add<Compare::CmpEq>();
        add<Compare::CmpGt>();
        add<Compare::CmpBracketed>();
        add<Compare::ZeroOperands>();
        add<Compare::OneOperand>();
        add<Compare::ThreeOperands>();
        add<Compare::IncompatibleTypes>();
        add<Compare::OptimizeConstants>();
        add<Compare::NoOptimizeCmp>();
        add<Compare::NoOptimizeNe>();
        add<Compare::NoOptimizeNoConstant>();
        add<Compare::NoOptimizeWithoutFieldPath>();
        add<Compare::NoOptimizeWithoutFieldPathReverse>();
        add<Compare::OptimizeEq>();
        add<Compare::OptimizeEqReverse>();
        add<Compare::OptimizeLt>();
        add<Compare::OptimizeLtReverse>();
        add<Compare::OptimizeLte>();
        add<Compare::OptimizeLteReverse>();
        add<Compare::OptimizeGt>();
        add<Compare::OptimizeGtReverse>();
        add<Compare::OptimizeGte>();
        add<Compare::OptimizeGteReverse>();

        add<Constant::Create>();
        add<Constant::CreateFromBsonElement>();
        add<Constant::Optimize>();
        add<Constant::Dependencies>();
        add<Constant::AddToBsonObj>();
        add<Constant::AddToBsonArray>();

        add<FieldPath::Invalid>();
        add<FieldPath::Dependencies>();
        add<FieldPath::Missing>();
        add<FieldPath::Present>();
        add<FieldPath::NestedBelowNull>();
        add<FieldPath::NestedBelowUndefined>();
        add<FieldPath::NestedBelowMissing>();
        add<FieldPath::NestedBelowInt>();
        add<FieldPath::NestedValue>();
        add<FieldPath::NestedBelowEmptyObject>();
        add<FieldPath::NestedBelowEmptyArray>();
        add<FieldPath::NestedBelowEmptyArray>();
        add<FieldPath::NestedBelowArrayWithNull>();
        add<FieldPath::NestedBelowArrayWithUndefined>();
        add<FieldPath::NestedBelowArrayWithInt>();
        add<FieldPath::NestedWithinArray>();
        add<FieldPath::MultipleArrayValues>();
        add<FieldPath::ExpandNestedArrays>();
        add<FieldPath::AddToBsonObj>();
        add<FieldPath::AddToBsonArray>();


        add<Or::NoOperands>();
        add<Or::True>();
        add<Or::False>();
        add<Or::TrueTrue>();
        add<Or::TrueFalse>();
        add<Or::FalseTrue>();
        add<Or::FalseFalse>();
        add<Or::FalseFalseFalse>();
        add<Or::FalseFalseTrue>();
        add<Or::ZeroOne>();
        add<Or::ZeroFalse>();
        add<Or::FieldPath>();
        add<Or::OptimizeConstantExpression>();
        add<Or::NonConstant>();
        add<Or::ConstantNonConstantTrue>();
        add<Or::ConstantNonConstantFalse>();
        add<Or::NonConstantOne>();
        add<Or::NonConstantZero>();
        add<Or::NonConstantNonConstantOne>();
        add<Or::NonConstantNonConstantZero>();
        add<Or::ZeroOneNonConstant>();
        add<Or::ZeroZeroNonConstant>();
        add<Or::Nested>();
        add<Or::NestedOne>();

        add<Strcasecmp::NullBegin>();
        add<Strcasecmp::NullEnd>();
        add<Strcasecmp::NullMiddleLt>();
        add<Strcasecmp::NullMiddleEq>();
        add<Strcasecmp::NullMiddleGt>();

        add<SubstrBytes::FullNull>();
        add<SubstrBytes::BeginAtNull>();
        add<SubstrBytes::EndAtNull>();
        add<SubstrBytes::DropBeginningNull>();
        add<SubstrBytes::DropEndingNull>();
        add<SubstrBytes::NegativeLength>();

        add<ToLower::NullBegin>();
        add<ToLower::NullMiddle>();
        add<ToLower::NullEnd>();

        add<ToUpper::NullBegin>();
        add<ToUpper::NullMiddle>();
        add<ToUpper::NullEnd>();

        add<Set::Same>();
        add<Set::Redundant>();
        add<Set::DoubleRedundant>();
        add<Set::Sub>();
        add<Set::Super>();
        add<Set::SameBackwards>();
        add<Set::NoOverlap>();
        add<Set::Overlap>();
        add<Set::FirstNull>();
        add<Set::LastNull>();
        add<Set::NoArg>();
        add<Set::OneArg>();
        add<Set::EmptyArg>();
        add<Set::LeftArgEmpty>();
        add<Set::RightArgEmpty>();
        add<Set::ManyArgs>();
        add<Set::ManyArgsEqual>();

        add<AllAnyElements::JustFalse>();
        add<AllAnyElements::JustTrue>();
        add<AllAnyElements::OneTrueOneFalse>();
        add<AllAnyElements::Empty>();
        add<AllAnyElements::TrueViaInt>();
        add<AllAnyElements::FalseViaInt>();
        add<AllAnyElements::Null>();
    }
};

SuiteInstance<All> myall;

namespace NowAndClusterTime {
TEST(NowAndClusterTime, BasicTest) {
    intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest());

    // $$NOW is the Date type.
    {
        auto expression = ExpressionFieldPath::parse(expCtx, "$$NOW", expCtx->variablesParseState);
        Value result = expression->evaluate(Document());
        ASSERT_EQ(result.getType(), Date);
    }
    // $$CLUSTER_TIME is the timestamp type.
    {
        auto expression =
            ExpressionFieldPath::parse(expCtx, "$$CLUSTER_TIME", expCtx->variablesParseState);
        Value result = expression->evaluate(Document());
        ASSERT_EQ(result.getType(), bsonTimestamp);
    }

    // Multiple references to $$NOW must return the same value.
    {
        auto expression = Expression::parseExpression(
            expCtx, fromjson("{$eq: [\"$$NOW\", \"$$NOW\"]}"), expCtx->variablesParseState);
        Value result = expression->evaluate(Document());

        ASSERT_VALUE_EQ(result, Value{true});
    }
    // Same is true for the $$CLUSTER_TIME.
    {
        auto expression =
            Expression::parseExpression(expCtx,
                                        fromjson("{$eq: [\"$$CLUSTER_TIME\", \"$$CLUSTER_TIME\"]}"),
                                        expCtx->variablesParseState);
        Value result = expression->evaluate(Document());

        ASSERT_VALUE_EQ(result, Value{true});
    }
}
}
}  // namespace ExpressionTests