I should have been clearer  - the full *python* test suite, not just IDLE, an with gui available -- "python -m test -ugui".  I don't think the check is applied with just one file, and definitely not with 'test.test_idle' versus 'test -ugui test_idle'.  The former runs test_idle with unittest.main instead of test.regrtest, which calls unittest.main but adds extra stuff.

Evading this issue is why I sometimes copy a method to be tested to a mock class with mock methods needed for the tested method.