Log expected & actual color in image access tests

[Yay295]

No description provided.

[hugovk]

Thanks, here's a variable naming suggestion.

[hugovk]

Thank you!

[radarhere]

If I break the test in main, I get

E       AssertionError: put/getpixel roundtrip failed for mode I;16B, color 32766
E       assert 32767 == 32766
E        +  where 32767 = <bound method Image.getpixel of <PIL.Image.Image image mode=I;16B size=1x1 at 0x104945F70>>((0, 0))
E        +    where <bound method Image.getpixel of <PIL.Image.Image image mode=I;16B size=1x1 at 0x104945F70>> = <PIL.Image.Image image mode=I;16B size=1x1 at 0x104945F70>.getpixel

If I break the test with this branch, I get

E       AssertionError: put/getpixel roundtrip failed for mode I;16, expected 32766 got 32767
E       assert 32767 == 32766

I can see that the argument that the 'where' lines being removed makes it tidier, but I'm not convinced that the values need to be part of the error message, as they're already listed in the next line?

It is listed in the summary now as

FAILED Tests/test_image_access.py::TestCffiGetPixel::test_signedness[32769-I;16B] - AssertionError: put/getpixel roundtrip failed for mode I;16B, expected 32768 got 32769

where the actual value wouldn't be listed otherwise. I'm not opposed to that, I just wonder if this is trying to fight against pytest's decision to have the summary not include more details.

[Yay295]

The only change is from "color 32766" to "expected 32766 got 32767". I don't think that's excessive for an error message. Also, if a message isn't provided to the assert, the summary message will be just "assert 32767 == 32766". So the current summary actually gives less information than the default.