The unsplittable_collections_on_random_shard_jscore_txns suite is testing transactions with unsplittable collections residing on arbitrary shards: the mongos is choosing a random dataShard before forwarding the createCollection request.

This feature is nevertheless incompatible with tests that include the creation of unsplittable collections within the scope of a transaction, since such a request can only be served by a primary shard.

Tests such as concurrent_drops_and_creates.js should not be executed under the suite.