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diff --git a/src/mongo/db/pipeline/window_function/window_function_min_max_test.cpp b/src/mongo/db/pipeline/window_function/window_function_min_max_test.cpp
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+/**
+ *    Copyright (C) 2021-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/db/exec/document_value/document_value_test_util.h"
+#include "mongo/db/pipeline/window_function/window_function.h"
+#include "mongo/db/query/collation/collator_interface_mock.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+class WindowFunctionMinMaxTest : public unittest::Test {
+public:
+    WindowFunctionMinMaxTest()
+        : collator(CollatorInterfaceMock::MockType::kToLowerString),
+          cmp(&collator),
+          min(cmp),
+          max(cmp) {}
+
+    CollatorInterfaceMock collator;
+    ValueComparator cmp;
+    WindowFunctionMin min;
+    WindowFunctionMax max;
+};
+
+TEST_F(WindowFunctionMinMaxTest, EmptyWindow) {
+    ASSERT_VALUE_EQ(min.getValue(), Value{BSONNULL});
+
+    ASSERT_VALUE_EQ(max.getValue(), Value{BSONNULL});
+}
+
+TEST_F(WindowFunctionMinMaxTest, SingletonWindow) {
+    min.add(Value{5});
+    ASSERT_VALUE_EQ(min.getValue(), Value{5});
+
+    max.add(Value{7});
+    ASSERT_VALUE_EQ(max.getValue(), Value{7});
+}
+
+TEST_F(WindowFunctionMinMaxTest, SmallWindow) {
+    min.add(Value{5});
+    min.add(Value{2});
+    min.add(Value{10});
+    min.add(Value{3});
+    ASSERT_VALUE_EQ(min.getValue(), Value{2});
+
+    max.add(Value{7});
+    max.add(Value{1});
+    max.add(Value{8});
+    max.add(Value{4});
+    ASSERT_VALUE_EQ(max.getValue(), Value{8});
+}
+
+TEST_F(WindowFunctionMinMaxTest, Removal) {
+    min.add(Value{5});
+    min.add(Value{2});
+    min.add(Value{10});
+    min.add(Value{3});
+    ASSERT_VALUE_EQ(min.getValue(), Value{2});
+
+    min.remove(Value{5});
+    ASSERT_VALUE_EQ(min.getValue(), Value{2});
+
+    min.remove(Value{2});
+    ASSERT_VALUE_EQ(min.getValue(), Value{3});
+}
+
+TEST_F(WindowFunctionMinMaxTest, Duplicates) {
+    min.add(Value{2});
+    min.add(Value{2});
+    min.add(Value{99});
+    min.add(Value{77});
+    ASSERT_VALUE_EQ(min.getValue(), Value{2});
+
+    // Removing one instance of the min isn't enough.
+    min.remove(Value{2});
+    ASSERT_VALUE_EQ(min.getValue(), Value{2});
+
+    // The min changes only once all instances are removed.
+    min.remove(Value{2});
+    ASSERT_VALUE_EQ(min.getValue(), Value{77});
+}
+
+TEST_F(WindowFunctionMinMaxTest, Ties) {
+    // When two elements tie (compare equal), remove() can't pick an arbitrary one,
+    // because that would break the invariant that 'add(x); add(y); remove(x)' is equivalent to
+    // 'add(y)'.
+
+    auto x = Value{"foo"_sd};
+    auto y = Value{"FOO"_sd};
+    // x and y are distinguishable,
+    ASSERT_VALUE_NE(x, y);
+    // but they compare equal according to the ordering.
+    ASSERT(cmp.evaluate(x == y));
+
+    min.add(x);
+    min.add(y);
+    min.remove(x);
+    ASSERT_VALUE_EQ(min.getValue(), y);
+
+    max.add(x);
+    max.add(y);
+    max.remove(x);
+    ASSERT_VALUE_EQ(max.getValue(), y);
+}
+
+}  // namespace
+}  // namespace mongo