Testing – unittest and doctest

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.