Tests runners support coverage plugins (to be installed via pip) that will provide useful information about what lines in the code have been executed while the tests were running. This information is of great help so that we know which parts of the code need to be covered by tests, as well identifying improvements to be made (both in the production code and in the tests). One of the most widely used libraries for this is coverage (https://pypi.org/project/coverage/).

While they are of great help (and we highly recommend that you use them and configure your project to run coverage in the CI when tests are run), they can also be misleading; particularly in Python, we can get a false impression if we don't pay close attention to the coverage report.