Cannot run single test anymore

[patnr]

I want the command pytest to run all tests. That's why the addopts in pyproject.toml is so long.

But now it seems impossible to run just a single tests using pytest tests/test_desired.py

So I think maybe the different purposes of testing (regular, doctests, coverage, etc) should be split, and made into different tox test environments.

This might complicate the travis setup... we'll see