The 'module' is a library of pay computation functions that your app uses privately. The library itself is public and could have other users, eg. you when invo

The 'module' is a library of pay computation functions that your app uses privately. The library itself is public and could have other users, eg. you when invoking manually from cli when testing things out. Test your library code with unit tests - this is easier because it can be done in isolation feom external systems. Itegration testing of apps is difficult. Often it is sufficient to test by use - have a dev environment which is usable or test in prod if it's not a critically important app. This is often sufficient, but I'm sure testing gurus have a recipe to apply unit tests to the app itself as well. I personally prefer not to have 10:1 test to code ratio, so I keep things practical.