I launched a 4.0 replica set with --storageEngine ephemeralForTest argument. The resulting replica set is much faster at running my tests, however it failed thusly on transactions tests:

     Mongo::Error::OperationFailure:
       Transaction numbers are only allowed on storage engines that support document-level locking (20)

This ticket is a request to support document level locking in ephemeralfortest storage engine, in order for it to be usable for transactions testing.