Measure test coverage in subshells

[zupo]

Some code needs to have # pragma: no cover so that our coverage still shows as 100%. The reason is this code is executed in a subshell while testing (using pexpect) so coverage doesn't pick it up.

coverage.py supports measuring subprocess execution but I am too tired at the moment to figure it out: https://coverage.readthedocs.io/en/6.2/subprocess.html