--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.

[rrlamichhane]

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

[kmuehlbauer]

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.