Please error when fixtures conflict

[smurfix]

The pytest_toolbox module also contains a caplog fixture, which broke a few of my tests. Finding that bug was no fun.

pytest should raise an error when it encounters conflicting fixtures.

[pytestbot]

GitMate.io thinks possibly related issues are #201 (conflicting option string(s): --fixtures), #2726 (pytest_generate_tests conflicts with conftest.py fixtures), #2201 (Doc error in fixtures section), #1098 (Confusing error message around tmpdir fixture), and #2934 (capsysbinary fixture).

[The-Compiler]

Overriding fixtures is also a feature, so I don't think that's possible.

[smurfix]

@The-Compiler Mark the overriding fixture as intentionally overriding, then. @pytest.mark.fixture_override or @pytest.mark.fixture(priority=True) would be two possible APIs for that.

[The-Compiler]

That'd be a possibility, with an appropriate deprecation period.

[flub]

Hmm, we don't mark fixtures, only test functions. But @pytest.fixture(replace=True) could be a possibility. Though coming up with a better name might be useful ;-)

This could make some plugins which provide the same fixture no longer co-installable though. Not sure if that exists in practice, the the lack of namespacing in fixtures doesn't make this too far fetched though. Making enabling this exclusion opt-in in pytest.ini might be a suitable solution though.

Would you mind having a go at a pull request for this? Feel free to ask questions! (also on freenode/#pylib on IRC)

[smurfix]

I'll see what I can do, though frankly the pytest internals are not easy to understand and my time is limited. :-/

[RonnyPfannschmidt]

@flub that topic in particular is so freakishly messy that i suspect 3-4 attempts each about 3-4 workdays are needed to sort out (marks was simpler)

[Zac-HD]

Closing this in favor of #3966, which has a more detailed plan for what we should do and warn about when overriding fixtures.