I tried out the instructions.  I guess my first question is how stand alone these instructions are and how much you expect someone to already know about coverage.  What I mean is, I needed to go to the devguide to read more about coverage in order to run the steps here.

For example, the devguide suggests creating a venv before running pip install coverage.  If I do that and go into the venv, then I could do (with python instead of ./python):

python -m coverage run --source Lib/idlelib Lib/idlelib/idle_test/test_config.py
python -m coverage report
python -m coverage html

Those steps seem to work.

Without the venv, ./python -m coverage doesn't work without the pip install (I get the 'No module named coverage' error).  At some point (as per the devguide), I had also downloaded the in-development version, so I am able to run 
./python ../coveragepy run --source Lib/idlelib Lib/idlelib/idle_test/test_config.py

At the time, the devguide suggested the in development version because it was more recent for 3.7 than the released version was, but it seems that the version on pip is the most current now.

Just like everything else, it seems that there are a few ways to go with this, but the venv with pip install seems to be the most foolproof.  I don't know if you'd also want to include instructions for running coverage over all of idle_test instead of just one module.


(without the ./python)