Unit testing is absolutely essential. If there's no automated test to show a particular element functionality, then the feature doesn't really exist. Put another way, it's not done until there's a test that shows that it's done.
We'll touch, tangentially, on testing. If we were to delve into testing each object-oriented design feature, the book would be twice as big as it is. Omitting the details of testing has the disadvantage that it makes good unit tests seem optional. They're emphatically not optional.
Unit testing is essential
When in doubt, design the tests first. Fit the code to the test cases.
Python offers two built-in testing frameworks. Most applications and libraries will make use of both. The general ...