mtest.CreateCollection will create a collection and only drop it after the test has finished running. The new unified spec test runner will drop the collection at the beginning of the test before creating it. This means that running a unified spec test before running a test that uses mtest.CreateCollection can potentially leave collections undropped between tests. Since the unified test format spec explicitly says to drop the specified collection and then create it, we should probably change mtest.CreateCollection to either do the same or drop the collection before and after test execution.