* Add a detailed console report to the 'test_coverage' command output
* Expand the precision of all coverage percentages to two decimal places
* Print the location of the HTML coverage report at the end of the console report
- Coverage should only be required if running tests
- When running test_coverage command all the install dependencies and
test dependencies should be installed.
- 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