Add a coverage plugin that handles ipykernel cells

[chmp]

Open issues:

• how to inject the coverage plugin with a coveragerc file?
  • document the standard way (using .coveragerc)
• how to get coverage to not ignore the (non-existing) kernel directory?
  • For cell files of such as C:/Users/{USER}/AppData/Local/Temp/ipykernel_1300/3920661193.py, C:/Users/{USER}/AppData/Local/Temp works, C:/Users/{USER}/AppData/Local/Temp/ipykernel_1300 does not
  • theory this behavior is triggered by this line
  • A: without explicit source, this issue does not come up
• Another issue is that %%ipytest --cov gets completed to %%ipytest --cov {MODULE}. Therefore {MODULE} is added to the sources. Using %%ipytest --cov -vv works correctly.
  • A: insert a -- in the defopts to make sure the inserted module is never parsed an argument value

Notes:

• ipykernel uses a custom caching compiler (source)
• this caching compiler uses a file of the format {TMP_PATH}/ipykernel_{pid}/{code_hash}.py (source)

[westurner]

Thanks. Line and Branch Coverage help check code quality.

Common misconception: if something has 100% test coverage, it's also fuzzed.

also, re: hypothesis property testing and pytest-cov: https://hypothesis.readthedocs.io/en/latest/strategies.html#interaction-with-pytest-cov

[westurner]

The %%file cell magic can be used to create files like .coveragerc from a notebook.

%%file .coveragerc
[run]
plugins =
    ipytest.cov

Would an ipytest.generate_coveragerc() or similar be too much? or Just autoconfig(coverage=True) or something?

[chmp]

TBH. I would rather prefer, that there is an option to configure pytest-cov programatically and inject the plugin in that way. I will open an issue for further discussion.