Use more pytest fixtures in modules tests

[fabianegli]

This PR adds some fixtures to pytest via the conftest.py file in the tests directory. They can then be reused throughout the test suite and as a proof of concept are applied here for some tests of the modules command.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

Merging #2226 (a935cae) into dev (27318f1) will increase coverage by 0.04%.
The diff coverage is n/a.

❗ Current head a935cae differs from pull request most recent head fef797d. Consider uploading reports for the commit fef797d to get more accurate results

@@            Coverage Diff             @@
##              dev    #2226      +/-   ##
==========================================
+ Coverage   73.02%   73.06%   +0.04%     
==========================================
  Files          78       78              
  Lines        8384     8384              
==========================================
+ Hits         6122     6126       +4     
+ Misses       2262     2258       -4     

see 2 files with indirect coverage changes

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[mirpedrol]

Looks very good :)
Is your idea to move all tests to using fixtures before merging? Or would you rather start with this as a POC?

[mirpedrol]

We will probably need to split it into separate fixtures. For the tests you have implemented we only need the modules repo, but for example to test installing modules we will need the installation objects.

[fabianegli]

True. But normally I try to go a step as small as possible. Splitting it up will be a later step when it is needed.

[fabianegli]

I would start small and go step by step to gain experience with the fixtures in relation to side effects created by tools and git. Otherwise we'll end up with a big PR and if possible I'd like to avoid that.

[fabianegli]

I added the WIP label, because it doesn't yet behave as I initially expected it to. While the return values of fixtures are fixed, side effects are not. There needs to be some other handling of this. I was lately looking into in-memory file systems to see if we could speed up by caching repo states in memory to speed up tests, but I haven't had the spare time required to investigate the options. One specific idea is to use pytest-pyfakefs.

[mirpedrol]

sounds good! will have a look to pyfakefs, thanks :)