Let scripted side_effect sequences absorb surplus mock calls#578
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An exact-length side_effect=[...] list raises StopIteration the moment the mocked call happens once more than the test scripted, which on a loaded host presents as an unrelated failure with no useful traceback. Add tests/_mock_effects.repeat_last, which chains the scripted effects into an endless repeat of the last one, and convert the 18 list-literal sites so a surplus call now trips the test's own assertions instead. The two PropertyMock sites in the catalog tests script a get followed by a raising set; those become a callable (any get reports the current tab, any set raises like Textual's active validator) since tail-repeating would make a surplus read raise the setter's error.
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Problem
Eighteen tests script mocks with an exact-length
side_effect=[...]list. The moment the mocked call happens once more than the author assumed, the list exhausts and raises StopIteration, which presents as an unrelated failure with no useful traceback. On a loaded CI host that extra call is exactly what happens: the Windows 3.12 lane has failed this way on a fully mocked test whose only upstream change was comment text.Solution
Add a small shared helper,
tests/_mock_effects.repeat_last, which chains the scripted effects into an endless repeat of the last one, and convert all 18 list-literal sites to it. A surplus call now returns the last scripted value and the test fails, if at all, on its own assertions with a readable diff. The two PropertyMock sites in the catalog tests script a get followed by a raising set, so they become a callable instead: any get reports the current tab and any set raises the way Textual's active validator does, however many times the code under test retries.