Add codecov and coverage threshold, hoist test requirements to setup.py

[bollwyvl]

motivated by #346 (comment)

• adds docs/requirements.txt to MANIFEST.in
• reads the requirements file during build for [test]
• adds a [coverage] with codecov and pytest-cov
• adds a coverage threshold (set to the current value) to fail in CI
• uploads to codecov at the end of a CI run (only the first fail will upload, however, due to fail-fast (which is fine))

  • the reports get (more) useful once merged to HEAD,

  • and it can be configured for badges, posting a report to PRs, etc.

• cache wheels and node_modules

  • appears to knock off ~30s

[bollwyvl]

Here's a build that shows the coverage threshold having teeth:
https://github.com/pydata/pydata-sphinx-theme/pull/348/checks?check_run_id=2193936885

[bollwyvl]

No further changes planned, can happily be squashed.

[choldgraf]

What is the purpose of this if statement, assuming that always is always true?

[choldgraf]

This looks great! One quick question

[bollwyvl]

If the test job fails, it wouldn't normally run the coverage upload task, the always makes sure it does. Having coverage from a fail isn't _too_ useful, in most cases, but since GitHub doesn't really have any test aggregation capabilities (like azure pipes) this leaves at least _some_ record of the tests having been run.

[jorisvandenbossche]

Thanks, looks good!

[jorisvandenbossche]

And we have a coverage overview now ;) https://codecov.io/gh/pydata/pydata-sphinx-theme/src/master/pydata_sphinx_theme/__init__.py