As the code we work on becomes complex, it is of extreme importance to pay attention to its maintainability. While everyone can easily learn how to write code, not everyone learns how to write maintainable code. One of the difficulties that are encountered when the code base grows is unexpected effects of local changes. It is quite common that a programmer changes a piece of code not realizing that it is also being used somewhere else. As a result, part of the application no longer works correctly, and the programmer is often not even aware of that. You already practiced writing several tests in Task $4$ of Unit $1$ using simple assert statements. Here, you will practice use of common Python tools to streamline the testing and ensure $100\%$ test coverage of your code base.