Provide a way for pytester to run coverage on plugins

[pytestbot]

Originally reported by: David MacIver (BitBucket: david_maciver_, GitHub: david_maciver_)

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Scenario: I am writing a pytest plugin. I want to get coverage information on my plugin's execution.

Unfortunately right now this is hard. The problem is that because the plugin is run in a subprocess, it's not actually included in the coverage run, so all the code in my plugin reports as uncovered even if it's actually run.

To fix this right now I have to go through a bit of a song and dance to get coverage to automatically execute on all python subprocesses using a sitecustomize file or a .pth file, neither of which are ideal (they're quite hard to set up in my CI environment). It would be really helpful if I could configure pytester with a hook to execute before loading python so that coverage would be provided for the subprocesses as well.

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• Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/675

[asottile]

@DRMacIver (since I assume this is you!) -- I've used this in the past. It sets up the .pth file described here.

The tl;dr is described in the pypi description

An example where I've used this: sass/libsass-python@6ff7491

(or https://github.com/asottile/setuptools-golang)

most of the magic is setting the COVERAGE_PROCESS_START environment variable pointing at the .coveragerc -- if your tests chdir you may need to set some additional variables to hint about where to write the .coverage files (can be seen as TOP substitution in setuptools-golang)

[blueyed]

Closing as answered.

[blueyed]

Well, maybe there is something that pytester could do - but only when testdir is used etc I guess.