warning "Module x was never imported" when running with xdist

[anthrotype]

If I install pytest-xdist plugin, and run pytest --cov with some -n number of parallel processes (even with -n 1), I get this warnings at the end:

Coverage.py warning: Module psautohint was never imported. (module-not-imported)
Coverage.py warning: No data was collected. (no-data-collected)

However, the data is collected, the .coverage.* data file is created, and a report is printed correctly despite the warnings.

If I run without passing the -n xdist option, so not in parallel, I don't get any such warnings.
Similarly I don't get those warning if I run coverage run -m pytest instead of pytest --cov.

I have a .coveragerc file in the root of the repository which contains this:

source = psautohint

[paths]
source =
    src/psautohint
    .tox/*/lib/python*/site-packages/psautohint
    .tox/*/lib/site-packages/psautohint
    .tox/pypy*/site-packages/psautohint

[anthrotype]

I'm using an src layout to avoid implicit import: the package named psautohint is not at the root of the repository, where .coveragerc and tox.ini are located, but it is inside the 'src' subfolder.

According to coverage docs, the source option in .coveragerc file can be either a filesystem path or the import name of a package. In my case it is the latter.

I use the paths option to treat all those listed as equivalent when combining coverage.

This always worked fine when running coverage run --parallel-mode -m pytest, followed by a final coverage combine (and codecov to upload the report).

I would like to try using pytest-cov plugin, but that warning tells me I may be doing something wrong?

[ionelmc]

How can I reproduce this? Enough to checkout https://github.com/adobe-type-tools/psautohint and run tox-something?

[anthrotype]

thanks for looking into this. Yes, you can just clone and run tox, you should get a warning like this
https://travis-ci.org/adobe-type-tools/psautohint/jobs/414896624#L498

[ionelmc]

Check the new examples from #267 - they should clarify how to correctly use pytest-cov in your project.

[anthrotype]

Thank you!