gh-106368: Argument clinic: add tests for more failure paths

[AlexWaygood]

And fix a minor bug I discovered along the way.

This gets us up to 95% coverage.

• Issue: Increase Argument Clinic test coverage #106368

[erlend-aasland]

Looks good. BTW, can you remove test_parameters_required_after_depr_star (line 1471)? I introduced an equal named, but slightly better test in #95151). Makes sense to bake it into this PR, rather than creating a new PR specifically for that removal.

[AlexWaygood]

Looks good. BTW, can you remove test_parameters_required_after_depr_star (line 1471)? I introduced an equal named, but slightly better test in #95151). Makes sense to bake it into this PR, rather than creating a new PR specifically for that removal.

Hmm, the new test that you added fails if I remove test_parameters_required_after_depr_star on line 1471. The new test method that you added is currently never run, because it is immediately overridden by the old test method later on in the class definition before unittest even tries to run any of the tests.

We really need to start running pyflakes on Tools/clinic/ and test_clinic.py in CI :)

[erlend-aasland]

Well, remove the new test, then 😄