Measure the test coverage

[yakutovicha]

fixes #440

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@ca48cc4). Click here to learn what that means.
Patch has no changes to coverable lines.

❗ Current head 18094f5 differs from pull request most recent head 322ea71. Consider uploading reports for the commit 322ea71 to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #441   +/-   ##
=========================================
  Coverage          ?   39.21%           
=========================================
  Files             ?       18           
  Lines             ?     3091           
  Branches          ?        0           
=========================================
  Hits              ?     1212           
  Misses            ?     1879           
  Partials          ?        0           

Flag	Coverage Δ
python-3.10	39.21% <0.00%> (?)
python-3.8	39.22% <0.00%> (?)
python-3.9	39.22% <0.00%> (?)

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[yakutovicha]

Since the reported coverage is well beyond my original goal of 10-15% (as stated in the issue), I am making this PR ready for the review.

[unkcpz]

I think we don't need this for these two tests. Even in aiida-core tests this fixture is not used very often. From my experience only when the aiida node stored in DB will break or mess up the logic of other tests.
Nevermind, I see for the second test it requires the database to be empty. This is needed.

[unkcpz]

@yakutovicha thanks for adding more tests! I have minor requests and things are not clear to me.

[unkcpz]

Looks all good.

[danielhollas]

@unkcpz @yakutovicha this is great, thanks! 👏