- Implement coverage functionality as a setuptools Command subclass
(in plinth/tests/coverage/test_coverage.py)
- Register the new 'test_coverage' command in setup.py
- Modify the INSTALL file to specify python3-coverage as a new dependency
- Modify the HACKING file to document the new 'test_coverage' command
- Have git (via .gitignore) ignore the '.coverage' output data file and
the contents of the 'plinth/tests/coverage/report' directory