Coverage is a boon: it lets you know how much of your code has tests and better, which lines in which files don't.
That comes at a price: instrumentation takes a while. You can speed
coverage by telling it to not look in places you don't care about:
your virtual environment's dependencies, your project's
.tox directories, etc. You'll also get more accurate percentages.
This is done with a
.coveragerc configuration file,
which has lots of options.
PyCharm though is finicky about this, hence this tip:
.coveragercfile in your project root
Make a run configuration to run your tests, and...
...edit that run configuration's working directory to start at the root