1 files changed, 39 insertions, 0 deletions
diff --git a/jstests/sharding/resharding_on_existing_key_is_noop.js b/jstests/sharding/resharding_on_existing_key_is_noop.js
new file mode 100644
index 00000000000..dcc3f68178e
--- /dev/null
+++ b/jstests/sharding/resharding_on_existing_key_is_noop.js
@@ -0,0 +1,39 @@
+/**
+ * Tests that trying to perform reshardCollection with a resharding key that matches the
+ * collection's existing shard key is a noop (which can be done by confirming the collection's UUID
+ * remains unchanged after the operation).
+ *
+ * @tags: [uses_atclustertime, requires_fcv_49,]
+ */
+(function() {
+"use strict";
+
+load("jstests/libs/uuid_util.js");
+load("jstests/sharding/libs/create_sharded_collection_util.js");
+
+const st = new ShardingTest({
+    mongos: 1,
+    config: 1,
+    shards: 2,
+    rs: {nodes: 2},
+});
+
+const sourceCollection = st.s.getCollection("reshardingDb.coll");
+
+CreateShardedCollectionUtil.shardCollectionWithChunks(sourceCollection, {key: 1}, [
+    {min: {key: MinKey}, max: {key: 0}, shard: st.shard0.shardName},
+    {min: {key: 0}, max: {key: MaxKey}, shard: st.shard1.shardName},
+]);
+
+const ns = sourceCollection.getFullName();
+const mongos = sourceCollection.getMongo();
+const sourceDB = sourceCollection.getDB();
+
+// The UUID should remain the same if the resharding key matches the existing shard key.
+const preReshardCollectionUUID = getUUIDFromListCollections(sourceDB, sourceCollection.getName());
+assert.commandWorked(mongos.adminCommand({reshardCollection: ns, key: {key: 1}}));
+const postReshardCollectionUUID = getUUIDFromListCollections(sourceDB, sourceCollection.getName());
+assert.eq(preReshardCollectionUUID, postReshardCollectionUUID);
+
+st.stop();
+})();