Undocumented method of fixture parametrization

[zack-alex]

This test passes:

import pytest


@pytest.fixture
def fixture(argument):
    return argument


@pytest.mark.parametrize("argument", ["foo", "bar"])
def test_with_argument(argument, fixture):
    assert argument == fixture


@pytest.mark.parametrize("argument", ["baz"])
def test_without_argument(fixture):
    assert "baz" == fixture

I failed to find any documentation on this argument passing technique.
Is it a supported and known feature or just a by-product of pytest.mark.parametrize implementation details?

My setup:

$ pip list | grep pytest
pytest                             3.8.0                                           
pytest-socket                      0.3.1

[zack-alex]

It looks almost like overriding a fixture with a parameter, except that in my case nothing is overridden (there is no fixture named "argument")

[RonnyPfannschmidt]

i believe its exactly that and we should elevate it to a actual feature

[nicoddemus]

i believe its exactly that and we should elevate it to a actual feature

Really? I personally find it quite confusing. Seems more like an unintended side-effect, which will be hard to carry over when we start refactoring the underlying fixture implementation.

[erheron]

Hi! Is there still a need to work on this issue?

[RonnyPfannschmidt]

@nicoddemus in that case we probably need to make the indirect a required argument there

as for fixtures, we will need to include a mechanism to distinguish between declared with params, declared as must be configured with params, declared as not having params (to enable better failing)

[nicoddemus]

@RonnyPfannschmidt just to be clear:

@pytest.mark.parametrize("argument", ["baz"], indirect=True)
def test_without_argument(fixture):
    assert "baz" == fixture

(indirect=["argument"] would also be valid)

I agree, if indirect not given we should raise an explicit error requiring indirect=True or indirect=["argument"].

Updated the labels to reflect that.

[erheron]

Hi! Could someone take a look at this commit on my fork of pytest?
I'm aware of fact this is far away from production-ready code, but just to check if the direction is right.
erheron@89086a1
The main issue is I don't really know where to put this enforcement we're talking about. Current proposition is _src/python.py, but I've started to think about _src/fixtures.py - for example function like _getnextfixturedef() raise FixtureLookupError when parameters are marked as indirect explicitly, so maybe this is the way to go?