Let's start our exploration with Python's built-in test library. This library provides a common interface for unit tests. Unit tests are a special kind of automated test that focuses on testing the least amount of code possible in any one test. Each test tests a single unit of the total amount of available code.
The Python library for this is called, unsurprisingly: unittest. It provides several tools for creating and running unit tests, the most important being the TestCase class. This class provides a set of methods that allow us to compare values, set up tests, and clean up after running them.
When we want to write a set of unit tests for a specific task, we create a subclass of TestCase, and write methods that accept no arguments to do the actual testing. These methods must all start with the string test. If this convention is followed, they'll automatically be run as part of the test process. Normally, the tests set some values on an object and then run a method, and use...