pytest_plugins in root conftest.py not working with tox

[fschulze]

Hi!

In devpi-server are several fixtures which are reused in plugin tests. That isn't optimal, see devpi/devpi#780. Some other fixtures are currently reused by importing them from test_devpi_server.conftest, some other with pytest_devpi_server which is a plugin with an entry point. The direct importing also seems to be bad for various reasons.

After trying for some time I managed to get it working by using pytest_plugins = ["pytest_devpi_server", "test_devpi_server.conftest"] in the root conftest.py of devpi-web.

Problem is, it only works when using pytest directly, not when using tox. I tried to debug it and am stuck. The modules are reached, which is confirmed by both tox -e py37 -- --trace-config and sprinkling pdb.set_trace() in them. All relevant modules pytest_devpi_server, test_devpi_server.conftest, web/conftest.py and web/tests/conftest.py are reached and included in the trace. Still the fixtures from test_devpi_server.conftest are not found when running tox, but work fine when using pytest directly.

[portyu9]

Hi @fschulze

I would avoid using another package's conftest.py itself as the reusable plugin.

Instead of:

pytest_plugins = [
    "pytest_devpi_server",
    "test_devpi_server.conftest",
]

move the shared fixtures into a normal importable module, for example:

test_devpi_server/fixtures.py

and load that:

pytest_plugins = [
    "pytest_devpi_server",
    "test_devpi_server.fixtures",
]

Or, better still, expose those fixtures from the actual pytest_devpi_server plugin if they belong to that plugin.

conftest.py has special pytest discovery and directory-scoping semantics, so treating one as a reusable cross-package plugin makes behavior unnecessarily dependent on how the source tree is laid out and imported. A normal plugin module avoids that ambiguity and behaves consistently from pytest and tox.

Since your --trace-config output says the modules are being loaded under tox, I would not conclude that tox simply failed to load pytest_plugins. The next useful diagnostic would be:

tox -e py37 -- pytest --fixtures -v

and compare whether the expected fixture names are actually registered and where pytest says they come from.

The robust fix is nevertheless to move reusable fixtures out of conftest.py and into a normal plugin module.

Please mark this answer as accepted if it helped, thank you.

[fschulze]

Thanks for taking the time to answer this. I already fixed it as you described about a year later. I hope this helps others as well.