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diff --git a/src/mongo/db/pipeline/expression_context_for_test.h b/src/mongo/db/pipeline/expression_context_for_test.h
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+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * 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
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * 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 GNU Affero General 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.
+ */
+
+#pragma once
+
+#include "mongo/db/pipeline/expression_context.h"
+
+namespace mongo {
+
+/**
+ * An ExpressionContext that can have state like the collation and resolved namespace map
+ * manipulated after construction. In contrast, a regular ExpressionContext requires the collation
+ * and resolved namespaces to be provided on construction and does not allow them to be subsequently
+ * mutated.
+ */
+class ExpressionContextForTest : public ExpressionContext {
+public:
+    ExpressionContextForTest() = default;
+
+    ExpressionContextForTest(OperationContext* txn, const AggregationRequest& request)
+        : ExpressionContext(txn, request, nullptr, {}) {}
+
+    /**
+     * Changes the collation used by this ExpressionContext. Must not be changed after parsing a
+     * Pipeline with this ExpressionContext.
+     */
+    void setCollator(std::unique_ptr<CollatorInterface> collator) {
+        ExpressionContext::setCollator(std::move(collator));
+    }
+
+    /**
+     * Sets the resolved definition for an involved namespace.
+     */
+    void setResolvedNamespace(const NamespaceString& nss, ResolvedNamespace resolvedNamespace) {
+        _resolvedNamespaces[nss.coll()] = std::move(resolvedNamespace);
+    }
+};
+
+}  // namespace mongo