Expert Python Programming - Third Edition

Unit tests

Unit tests are low-level tests that perfectly fit test-driven development. As the name says, they focus on testing software units. A software unit can be understood as the smallest testable piece of the application code. Depending on the application, the size may vary from whole modules to a single method or function, but usually unit tests are written for the smallest fragments of code possible. Unit tests usually isolate the tested unit (module, class, function, and so on) from the rest of the application and other units. When external dependencies are required, such as web APIs or databases, they are often replaced by fake objects or mocks.