Tests are skipped with pytest-xdist

pytest-dependency does not seem to behave well when using pytest-xdist. Some tests are skipped when they should not be. Let’s see how to quickly reproduce the bug:

test_foobar.py

import pytest

@pytest.mark.dependency()
def test_a():
    pass

@pytest.mark.dependency(depends=["test_a"])
def test_b():
    pass

console

virtualenv env
./env/bin/pip install pytest
./env/bin/pip install pytest-xdist
./env/bin/pip install pytest-dependency
./env/bin/pytest -n auto test_foobar.py

output

pytest test_foobar.py -n auto
============================= test session starts ==============================
platform linux -- Python 3.6.1, pytest-3.1.3, py-1.4.34, pluggy-0.4.0
rootdir: /home/eloi/dev/dependency-test, inifile:
plugins: xdist-1.18.1, dependency-0.2
gw0 [2] / gw1 [2] / gw2 [2] / gw3 [2]
scheduling tests via LoadScheduling
s.
===================== 1 passed, 1 skipped in 0.31 seconds ======================

[RKrahl]

I documented the incompatibility with the parallelization in pytest-xdist and closed this issue. However, this is not the full story: pytest-xdist 1.19 added distributing mode loadscope and 1.21 added loadfile. Both distributing modes are compatible with pytest-dependency under certain conditions. But these distributing modes are marked experimental in pytest-xdist. I will wait for them to become stable before documenting this option.

[pkoch]

@RKrahl Can we perhaps piggyback off of --dist loadgroup? If we make every connected test belong to their own group, that seems to compatibilize the interaction between the two packages, no?