In the case of pytest, we have to install the pytest-cov package (at the time of this writing, version 2.5.1 is used in this book). Once installed, when the tests are run, we have to tell the pytest runner that pytest-cov will also run, and which package (or packages) should be covered (among other parameters and configurations).
This package supports multiple configurations, like different sorts of output formats, and it's easy to integrate it with any CI tool, but among all these features a highly recommended option is to set the flag that will tell us which lines haven't been covered by tests yet, because this is what's going to help us diagnose our code and allow us to start writing more tests.
To show you an ...
