Regression in 2.6.0: running coverage combine after pytest-cov now errors out

We run coverage in parallel=True mode, because we have some tests that spawn subprocesses, and we want to capture coverage for all of them. To get a complete report for codecov, the CI does:

pytest --cov ...
coverage combine
bash <(curl -s https://codecov.io/bash)

As far as I know, this was mandatory on pytest-cov 2.5.1 and earlier. Since 2.6.0 came out yesterday, our tests have been failing because coverage combine says No data to combine and it errors out, failing the test suite.

I think this may be happening because pytest-cov is now effectively running coverage combine itself, so that instead of being mandatory to run coverage combine, it’s now mandatory to not to run coverage combine? Possibly because of changes in #178? For now that seems to be working for us. But it’d be nice to confirm that our understanding is correct, and I figured you’d rather have a heads-up than not.

Our bug: https://github.com/python-trio/trio/issues/646

[cjw296]

This auto-combine is problematic when you have several runs of pytest (say across different versions of python) and want to combine them. Please at least add an option to prevent pytest-cov doing this combining.

[cjw296]

Some that that could be put in .coveragerc or pytest.ini would be ideal.