The rollback_cmd_unrollbackable.js Javascript test creates an oplog entry of an unsupported format, inserts it into the oplog manually, and then tries to have a node roll back that oplog entry to check that it fasserts. This test case could be easily covered by a "death" test in our unit tests, in rs_rollback_test.cpp, for example.

Furthermore, we should probably try to move away from having integration tests that manually modify the oplog, since that is a behavior that should be disallowed, and is not something that we account for when designing and testing the replication system.