Commit https://github.com/mongodb/mongo/commit/279fba2819e281053b19507e06b862b852d4e85f removed the MultiApplyAssignsOperationsToWriterThreadsBasedOnNamespaceHash test because with the new StringMap implementation the internal hash produced is not deterministic between runs. See the corresponding change in sync_tail.cpp

Perhaps there's a way to re-write this test to not loose test coverage.
For more details, see the discussion in: https://mongodbcr.appspot.com/243700002/