[pytest-dev] no self-awareness for pytest

[Jason King]

> I'll give testpaths a go and see what happens.
> _______________________________________________

turns out I'd specified 'testpaths = tests' already in tox.ini

one thing I didn't make clear, running pytest.main() with the arguments 
I listed
earlier means that Its looking at the matplotlib install location, (ie 
in the site-packages dir,
inside the venv, next to where numpy is installed. (not where the files 
were unpacked from)