Reimplement fluidsim-test by just calling pytest
I don't use
fluidsim-test anymore but directly
pytest, which is just more convenient.
A problem is that there are differences between
pytest (stdout capture, test discovery).
Therefore, I think we need to reimplement something like
fluidsim-test but with just using
pytest programmatically, as explained here https://github.com/pytest-dev/pytest/issues/2544#issuecomment-312742145