1 files changed, 48 insertions, 0 deletions
diff --git a/jstests/multiVersion/prepare_unique_fcv_check.js b/jstests/multiVersion/prepare_unique_fcv_check.js
new file mode 100644
index 00000000000..7cf27162d64
--- /dev/null
+++ b/jstests/multiVersion/prepare_unique_fcv_check.js
@@ -0,0 +1,48 @@
+/* Test that an index that contains prepareUnique cannot be created when
+ * featureFlagCollModIndexUnique is not enabled.
+ *
+ * @tags: [requires_persistence]
+ */
+(function() {
+"use strict";
+
+const mongod = MongoRunner.runMongod();
+assert.neq(null, mongod, "mongod was unable to start up");
+const db = mongod.getDB("test");
+const admin = db.getSiblingDB("admin");
+const coll = db.test;
+try {
+    checkFCV(admin, "6.0");
+} catch (e) {
+    jsTestLog("Expecting FCV 6.0: " + tojson(e));
+    quit();
+}
+
+// createIndex with prepareUnique should work by default.
+assert.commandWorked(db.runCommand(
+    {createIndexes: coll.getName(), indexes: [{key: {a: 1}, name: 'a_1', prepareUnique: true}]}));
+// coll should be created implicitly.
+assert(Array.contains(db.getCollectionNames(), coll.getName()));
+
+// Downgrade FCV
+assert.commandWorked(coll.dropIndex({a: 1}));
+assert.commandWorked(db.adminCommand({setFeatureCompatibilityVersion: lastLTSFCV}));
+
+// Now createIndex with prepareUnique:true should fail on an existing collection.
+let res = db.runCommand(
+    {createIndexes: coll.getName(), indexes: [{key: {a: 1}, name: 'a_1', prepareUnique: true}]});
+assert.commandFailedWithCode(res, ErrorCodes.InvalidOptions);
+
+// createIndex with prepareUnique:true should also fail on a new collection.
+assert(coll.drop());
+res = db.runCommand(
+    {createIndexes: coll.getName(), indexes: [{key: {a: 1}, name: 'a_1', prepareUnique: true}]});
+assert.commandFailedWithCode(res, ErrorCodes.InvalidOptions);
+
+// Upgrade FCV and createIndex with prepareUnique should now work.
+assert.commandWorked(db.adminCommand({setFeatureCompatibilityVersion: latestFCV}));
+assert.commandWorked(db.runCommand(
+    {createIndexes: coll.getName(), indexes: [{key: {a: 1}, name: 'a_1', prepareUnique: true}]}));
+
+MongoRunner.stopMongod(mongod);
+})();