Detect misapplication of given to e.g. setup methods

[DRMacIver]

We have a new entry in the ongoing war between making Hypothesis impossible to misuse and the creativity of determined users. 😉

17:12 <doismellburning> Annotating `setUp` with `given` - is this a thing? Is it ScarySauce(TM)?
17:12 <@DRMacIver> It's not a thing
17:12 <@DRMacIver> I've no idea what would happen, but it would probably be hilariously confusing
17:13 <doismellburning> welp, it's in my codebase!
17:13 — @DRMacIver blinks
17:13 <doismellburning> cheers :)
17:15 <@DRMacIver> Maybe Hypothesis should error (with deprecation path) when @given is applied to methods that don't have "test" in the name
17:16 <doismellburning> that sounds like it might be useful
17:17 <@DRMacIver> Yeah
17:17 <@DRMacIver> Though I'm sure https://xkcd.com/1172/ applies
17:18 <doismellburning> lol
17:23 <@DRMacIver> Maybe I'll just check for setUp for now. I can't think of too many other cases where this would be a problem.

I'm not sure what quite the right level of checking is here. I feel like it's reasonable, especially with toy examples, to use @given on methods that aren't strictly tests, but I can't think of a good use for it being on setUp. Maybe we should just have a small blacklist of method names?

This should go through the usual deprecation -> error later path of course.

[Zac-HD]

I think the user error here isn't "@given on things without test in the name" - that would break use of non-English function names, or even just alternative test discovery conventions.

Instead, I'd look for "@given on methods on a subclass of unittest.TestCase, where the name is defined on unittest.TestCase".

It looks like we can do this in run_test_with_generator in given in core.py, by suitably cautious use of the __self__ attribute to get the class it's bound to, ismethod, and issubclass - it'll fit right in with the rest of core.py!

(update: nope, not that easy - the test isn't bound to any class at the point where it's decorated)