pytest_fixture_setup hook - fixtures can return None

[uSpike]

Hi, I was looking into implementing my own pytest_fixture_setup() and I noticed something interesting.

The hook is defined with @hookspec(firstresult=True) so, as the docstring describes it will stop at the first non-None result. However, it seems that this hook is supposed to return the return value of the fixture call, see https://github.com/pytest-dev/pytest/blob/master/_pytest/fixtures.py#L788. This is interesting, because a fixture could return None even though it has run. A trivial example:

The effect of this is that if I want to override pytest_fixture_setup() and not have it run again (from the internally defined hook), then I must return a non-None value. But, this may not reflect the actual value as returned from the fixture.

Am I missing something? Is this not a big deal? I think it's strange to return True even if it is not affecting my tests.

[RonnyPfannschmidt]

@uSpike thansk for coming out and making this weakness that is based on the structure of how the plug-in system works obvious

i believe we should try to document that pitfall
in terms of consistent typing this is indeed a big deal

however the general expectation for a fixture is to actually return something,
strictly speaking - fixtures are dependency injection, so a fixture that doesn't return/yield a dependency to be injected is not doing what its supposed to do