In test_prepare04.py there are two error messages defined:

conflictmsg = '/conflict between concurrent operations/'
preparemsg = '/conflict with a prepared update/'

but these are never used in any later code. These messages don't appear in any other tests so it isn't a copy/paste error. It seems like there was an intent to test a conflict that was never added.

This should be investigated and either remove the unused lines or add in a test case for those conflicts.