utilize coverage test contexts!

[ewdurbin]

this enables evaluating and storing coverage test contexts to know what tests touched what lines of code, handy!

[ewjoachim]

Note: I personally like the pytest-cov extension, and it lets us do this with a simple flag --cov-context=test. I'd say, let's switch to pytest-cov :)

https://pytest-cov.readthedocs.io/en/latest/contexts.html