gh-107862: Add roundtrip hypothesis tests to test_binascii

[sobolevn]

• Issue: [Meta] Research: what can we test with Hypothesis? #107862

[ambv]

Closing and re-opening to retrigger CLA checks. Sorry for the noise.

[hauntsaninja]

Thanks for working on this!

[hauntsaninja]

Wonder if unhexlify should also take a sep and bytes_per_sep argument

[sobolevn]

Btw, @rhettinger was against doing this.

[hauntsaninja]

I agree that we shouldn't rely on Hypothesis' strategies as a substitute for fixed tests.

But I think the implementation chosen for adding property based tests in CPython is quite sensible! None of the Hypothesis strategies run by default in our test suite. Hypothesis is stubbed out and simply used used as a DSL to write property based tests where @hypothesis.example is used to provide the fixed test cases. However, if we wish, we can opt-in to get the real non-stub Hypothesis to run its strategies against the already written test because it's in a DSL it understands.

For this specific PR, I guess maybe I should have asked Nikita to add some specific @hypothesis.example here. Raymond, I'm happy to open a PR adding examples, or to revert, or to let it be. Just let me know!

(I also obviously agree we shouldn't use Hypothesis to write tests to enforce properties that are not actually properties, like the colorsys example)