"Module already imported so cannot be rewritten" warning with COV_CORE_SOURCE

[blueyed]

I am using the following in pytest-django's tox.ini (via the suggestion in pytest-dev/pytest-django#412 (comment)):

COV_CORE_SOURCE={toxinidir}
COV_CORE_CONFIG={toxinidir}/.coveragerc
COV_CORE_DATAFILE={toxinidir}/.coverage.eager

However, this requires to unset COV_CORE_SOURCE for the inner test runs
(which uses runpytest_subprocess).

I've noticed this because of a warning from pytest:

Module already imported so cannot be rewritten: pytest_cov

This warning however is still triggered by the outer pytest.

It makes sense, but I wonder if there is a better way to load pytest-cov eagerly by now (mentioned in the thread with #412), or if I should just configure the outer pytest to ignore this warning?

Related issue #148.