Remove py and pytest-forked test dependencies

[AlexWaygood]

We don't use either of these in our own code at all. Neither of them should be needed in 2023.

py used to be a dependency of pytest but no longer is. It was added to test-requirements.txt 6 years ago in order to pin a specific version to fix an issue where some tests were failing: 5168c25 and ad6dd4e.

pytest-forked used to be a dependency of pytest-xdist, but no longer is. It was added to test-requirements.txt` 4 years ago in order to pin a specific version to fix builds on macOS: e006b94.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[sobolevn]

For some reason master branch failed: https://github.com/python/mypy/actions/runs/5355970406/jobs/9714896673

[AlexWaygood]

For some reason master branch failed: https://github.com/python/mypy/actions/runs/5355970406/jobs/9714896673

I saw. I don't understand why that happened, given that all the tests passed on this PR. Looking into it now to see if the environment somehow changed between the PR runs of the tests and the runs of the tests on master.

[bluetech]

It looks like it's due to pytest 7.4.0 which I had just released. Looks like it's using a private API which broke (probably by me...).

[AlexWaygood]

It looks like it's due to pytest 7.4.0 which I had just released. Looks like it's using a private API which broke (probably by me...).

I reached the same conclusion simultaneously :) For now we can pin to pytest <7.4.0, and figure out how to migrate off the private API later.

We can see in the freeze step that the PR run used pytest 7.3.2: https://github.com/python/mypy/actions/runs/5355631169/jobs/9714141396

and the master run used pytest 7.4.0: https://github.com/python/mypy/actions/runs/5355970406/jobs/9714895421

[AlexWaygood]

#15505 should hopefully get things green again! 🤞

[bluetech]

Alternatively, a quick fix (untested) would be to change

self.parent._prunetraceback(excinfo)

to

if pytest.version_info >= (7, 4):
    excinfo.traceback = self.parent._traceback_filter(excinfo)
else:
    self.parent._prunetraceback(excinfo)

I don't have time ATM to provide a more proper solution which doesn't use private API, but I can look into it later.

[AlexWaygood]

Alternatively, a quick fix (untested)

I think I favour just adding a pin and a TODO for now, until we can come up with a more principled fix, but thank you!!

[AlexWaygood]

(Basically just a note to myself): this is the pytest commit that removed the _prunetraceback method: pytest-dev/pytest@fcada1e -- PR pytest-dev/pytest#10921.

Alternatively, a quick fix (untested) would be to change

self.parent._prunetraceback(excinfo)

to

if pytest.version_info >= (7, 4):
    excinfo.traceback = self.parent._traceback_filter(excinfo)
else:
    self.parent._prunetraceback(excinfo)

I don't think this exact snippet will work for mypy, as the second branch won't type check if pytest >=7.4 is installed. There are ways round that (type: ignore; use hasattr() instead of pytest.version_info; etc.), but we could also just bump our pytest lower bound to >=7.4, I think.

But the best solution would be if we could do our tests while using only pytest's public API, of course :)

[bluetech]

But the best solution would be if we could do our tests while using only pytest's public API, of course :)

I guess the first thing to understand is if there's anything wrong with doing

-            self.parent._prunetraceback(excinfo)
-            excrepr = excinfo.getrepr(style="short")
+            excrepr = super().repr_failure(excinfo, style)

BTW, since this is mypy 😄 , I'd mention that if you bump the pytest req to >=7.0.0 then you can type the excinfo parameter as pytest.ExceptionInfo[BaseException].

[AlexWaygood]

I guess the first thing to understand is if there's anything wrong with doing

-            self.parent._prunetraceback(excinfo)
-            excrepr = excinfo.getrepr(style="short")
+            excrepr = super().repr_failure(excinfo, style)

Pfff, no idea really! I dug through git blame, and it looks like we've been using this private API since we first adopted pytest in 2016: #1944. I don't know much about this area of mypy's codebase or much about pytest internals, I'm afraid!

@ikonst, you've been doing some great work improving mypy's test infrastructure recently -- any thoughts on this from you? :)

[mtelka]

-            self.parent._prunetraceback(excinfo)
-            excrepr = excinfo.getrepr(style="short")
+            excrepr = super().repr_failure(excinfo, style)

I tested this on OpenIndiana with pytest 7.4.0 and both Python 3.7.16 and 3.9.16 and all tests passed.

[sobolevn]

@mtelka please send a PR :)

[JukkaL]

I don't remember why we are using the private API, but I suspect it may be about ensuring tracebacks on test failure use a specific style or do/don't include certain entries. Tests passing may not be enough to validate things work. Manually checking the contents of a traceback when a test fails would be useful.

[mtelka]

@mtelka please send a PR :)

Sorry, I'm neither author of that change nor I do fully understand all consequences of the change (see #15501 (comment)), so I won't create a PR. I just wanted to report testing success.