Ensure COV_CORE_SRC is an absolute path before exporting to the environment

[ctheune]

Summary

When COV_CORE_SRC is a relative directory and a subprocess first changes its working directory
before invoking Python then coverage won't associate the

Expected vs actual result

Get proper coverage reporting, but coverage is not reported properly.

Reproducer

• specifiy the test directory with a relative path, i.e. bin/py.test src
• Create wrap a subprocess call in a shell script that first changes its work directory before calling bin/python src/something.py

Versions

Output of relevant packages pip list, python --version, pytest --version etc.

Python 3.8.5
pytest 6.1.2
pytest-asyncio==0.14.0
pytest-cache==1.0
pytest-cov==2.11.1
pytest-flake8==1.0.6
pytest-timeout==1.4.2

Config

Include your tox.ini, pytest.ini, .coveragerc, setup.cfg or any relevant configuration.

[run]
branch = True

[pytest]
addopts = --timeout=30 --tb=native --cov=src --cov-report=html src -r w
markers = slow: This is a non-unit test and thus is not run by default. Use ``-m slow`` to run these, or ``-m 1`` to run all tests.
log_level = NOTSET


filterwarnings =
    ignore::DeprecationWarning:telnetlib3.*:

Code

See https://github.com/flyingcircusio/backy/blob/master/src/backy/tests/test_backy.py#L99

I'm currently working around this by explicitly making COV_CORE_SRC absolute before calling the subprocess. I guess this could/should be done in general, too.

    os.environ['COV_CORE_SOURCE'] = os.path.abspath(
        os.environ['COV_CORE_SOURCE'])

[masenf]

Have you tried changing --cov=src to --cov=backy?

In my experiements, I found that subprocess coverage reporting works better when specifying source packages instead of filesystem paths.

In my case, this wasn't easy using a "flat" repo structure where the package directory (relative to repo root) and the package name are the same string. coverage.py seems to prefer interpreting blah as a filesystem path (if it exists), even if blah might be a package name.

A solution is to explicitly use source_pkgs = in the [coverage:run] section of the config file, and then simply pass --cov to pytest