1 files changed, 101 insertions, 0 deletions
diff --git a/jstests/core/ddl/collmod_convert_to_unique_violations.js b/jstests/core/ddl/collmod_convert_to_unique_violations.js
new file mode 100644
index 00000000000..53b8abeec6e
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+++ b/jstests/core/ddl/collmod_convert_to_unique_violations.js
@@ -0,0 +1,101 @@
+/**
+ * Tests that the CannotConvertIndexToUnique error returned when collmod fails to convert an index
+ * to unique contains correct information about violations found.
+ *
+ * @tags: [
+ *  # Cannot implicitly shard accessed collections because of collection existing when none
+ *  # expected.
+ *  assumes_no_implicit_collection_creation_after_drop,  # common tag in collMod tests.
+ *  requires_fcv_52,
+ *  requires_non_retryable_commands, # common tag in collMod tests.
+ *  # TODO(SERVER-61182): Fix WiredTigerKVEngine::alterIdentMetadata() under inMemory.
+ *  requires_persistence,
+ *  # The 'prepareUnique' field may cause the migration to fail.
+ *  tenant_migration_incompatible,
+ * ]
+ */
+
+(function() {
+'use strict';
+
+load("jstests/libs/feature_flag_util.js");
+load("jstests/libs/fixture_helpers.js");  // For 'isMongos'
+
+if (!FeatureFlagUtil.isEnabled(db, "CollModIndexUnique")) {
+    jsTestLog('Skipping test because the collMod unique index feature flag is disabled.');
+    return;
+}
+
+function sortViolationsArray(arr) {
+    // Sorting unsorted arrays of unsorted arrays -- Sort subarrays, then sort main array by first
+    // key of subarray.
+    for (let i = 0; i < arr.length; i++) {
+        arr[i].ids = arr[i].ids.sort();
+    }
+    return arr.sort(function(a, b) {
+        if (a.ids[0] < b.ids[0]) {
+            return -1;
+        }
+        if (a.ids[0] > b.ids[0]) {
+            return 1;
+        }
+        return 0;
+    });
+}
+
+const collName = 'collmod_convert_to_unique_violations';
+const coll = db.getCollection(collName);
+coll.drop();
+
+// Checks that the violations match what we expect.
+function assertFailedWithViolations(keyPattern, violations) {
+    // First sets 'prepareUnique' before converting the index to unique.
+    assert.commandWorked(
+        db.runCommand({collMod: collName, index: {keyPattern: keyPattern, prepareUnique: true}}));
+    const result =
+        db.runCommand({collMod: collName, index: {keyPattern: keyPattern, unique: true}});
+    assert.commandFailedWithCode(result, ErrorCodes.CannotConvertIndexToUnique);
+    assert.eq(
+        bsonWoCompare(sortViolationsArray(result.violations), sortViolationsArray(violations)),
+        0,
+        tojson(result));
+    // Resets 'prepareUnique'.
+    assert.commandWorked(
+        db.runCommand({collMod: collName, index: {keyPattern: keyPattern, prepareUnique: false}}));
+}
+
+assert.commandWorked(db.createCollection(collName));
+
+// Create regular indexes and try to use collMod to convert them to unique indexes.
+assert.commandWorked(coll.createIndex({a: 1}));
+assert.commandWorked(coll.createIndex({a: 1, b: 1}));
+
+// Conversion should fail when there are existing duplicates, reporting correct number of
+// violations.
+assert.commandWorked(coll.insert({_id: 1, a: 100, b: 1}));
+assert.commandWorked(coll.insert({_id: 2, a: 100, b: 2}));
+assertFailedWithViolations({a: 1}, [{ids: [1, 2]}]);
+
+assert.commandWorked(coll.insert({_id: 3, a: 100, b: 3}));
+assertFailedWithViolations({a: 1}, [{ids: [1, 2, 3]}]);
+
+assert.commandWorked(coll.insert({_id: 4, a: 101, b: 4}));
+assertFailedWithViolations({a: 1}, [{ids: [1, 2, 3]}]);
+
+assert.commandWorked(coll.insert({_id: 5, a: 105, b: 5}));
+assert.commandWorked(coll.insert({_id: 6, a: 105, b: 6}));
+assertFailedWithViolations({a: 1}, [{ids: [1, 2, 3]}, {ids: [5, 6]}]);
+
+// Test that compound indexes work as expected.
+assert.commandWorked(coll.insert({_id: 7, a: 105, b: 6}));
+assertFailedWithViolations({a: 1, b: 1}, [{ids: [6, 7]}]);
+
+assert.commandWorked(coll.insert({_id: 8, a: 105, b: 6}));
+assertFailedWithViolations({a: 1, b: 1}, [{ids: [6, 7, 8]}]);
+
+assert.commandWorked(coll.insert({_id: 9, a: 101, b: 4}));
+assertFailedWithViolations({a: 1, b: 1}, [{ids: [4, 9]}, {ids: [6, 7, 8]}]);
+
+assert.commandWorked(coll.insert({_id: "10", a: 101, b: 4}));
+assertFailedWithViolations({a: 1, b: 1}, [{ids: [4, 9, "10"]}, {ids: [6, 7, 8]}]);
+})();