Message 211639 - Python tracker

I concur that this is a regression - "     

unittest.expectedFailure()

    Mark the test as an expected failure. If the test fails when run, the test is not counted as a failure.
"

is in the public docs for the unittest module, and depending on a private attribute to be set is a bit of an abstraction violation - at the least it should handle it not being set (for any older test unittest compatible testcase object).