There are places the MongoDB Server test harness looks for explicit, hard-coded error messages from WiredTiger, which is more fragile than it should be, it would be great to not depend on specific error message wording:

src/mongo/db/storage/kv/kv_engine_test_harness.cpp:invariant(false, "commit timestamp is less than the oldest timestamp");
invariant(false, "commit timestamp is less than the stable timestamp");