[MNT] Test coverage and badges

[matteobachetti]

More of a recommendation than a requirement, but:

A convenient way to always have test coverage measurements is using https://about.codecov.io/ or similar services. They provide hooks to run coverage measurements each time you do tests through Github Actions (and point to the parts of the code that still have received no tests).

Codecov and many other services also provide convenient badges to show the health status of your code (see a good example here: https://github.com/astropy/astroquery), including coverage.

[xragua]

Thanks for the info, now I use codecov in my CI tests