pytest-cov: --cov and xdist missing coverage

Running pytest-cov with xdist (py.test -n auto --cov --cov-report=html) shows a warning at the end of the test run (Coverage.py warning: No data was collected) and reports 26431/73593 covered statements versus running without xdist (py.test --cov --cov-report=html) which reports 36879/73593 covered statements.

Versions:

coverage==4.2 pytest-cov==2.3.1 pytest==2.9.2 pytest-xdist==1.15.0

.coveragerc

[run]
source = dir1,dir2,dir3,dir4
branch = True
parallel = True

[report]
# Regexes for lines to exclude from consideration
exclude_lines =
    # Have to re-enable the standard pragma
    pragma: no cover

    # Don't complain if non-runnable code isn't run
    if __name__ == .__main__.:

    # Don't complain about uncovered code in tests that were supposed to fail
    @pytest.mark.xfail

# Always show line numbers of uncovered statements
show_missing = True

I’m going to work on a reproducible sample, but I’m hoping there’s some obvious config error here.

About this issue

Original URL
State: open
Created 8 years ago
Reactions: 2
Comments: 31 (13 by maintainers)

Commits related to this issue

This isn't working, and there isn't anything helpful in the github issue https://github.com/pytest-dev/pytest-cov/issues/129 — committed to william-richard/chili-pepper by william-richard 5 years ago

Most upvoted comments

I ran into this issue when I decided to introduce parallelization to our test-suite. @kmuehlbauer 's fix totally works. This issue should be closed with that remark:

# .coveragerc
[run]
concurrency = multiprocessing
parallel = true

rrlamichhane on Nov 5, 2020

I just came across this via github search. In my case I had to export COVERAGE_PROCESS_START=/path/to/.coveragerc and using the folowing lines to my .coveragerc:

[run]
concurrency = multiprocessing
parallel = true

Then xdist worked correctly together with cov.

kmuehlbauer on Mar 25, 2019

@ionelmc sorry for the long delay. I believe I found out what was going wrong.

Today we tested building the project with the latest release 2.7.1 (no pytest-xdist used nor installed) and the issue remained: sometimes the build failed with the message No data to report though there were coverage data printed to the terminal.

We then added pytest-xdist and used the workaround proposed by @kmuehlbauer. It worked like a charm.

Our CI system was running integration tests and unit tests at the same time and I believe that this parallel execution was messing up things for pytest-cov. pytest-xdist with the mentioned configurations may have guarded pytest-cov from race conditions.

allrod5 on May 22, 2019

Oooof … I would need help with small reproducers on the latest pytest-cov release. Pretty sure people are having different problems here.

ionelmc on Jan 23, 2019

@thedrow not sure what you’re asking. Besides having a different project layout there’s aliasing configuration (http://coverage.readthedocs.io/en/latest/config.html#paths). The issue of tardy coverage start I will fix sometime this month I hope.

ionelmc on Oct 6, 2017