Test-Driven Development in Python

Tests that arrive after the code break on every refactor, and tests that need a database to check a rounding rule make developers stop running the suite. This book works the other way round. Through one small, fully worked online shop, you practise the red-green-refactor loop in steps that stay small, write unit tests that describe behaviour, and use pytest fixtures and parametrization to remove repetition. You learn when stubs, fakes, spies and mocks fit, how autospec and patching go wrong, and how to design code so that clocks, files, environment variables and logs are easy to control. Later chapters cover keeping the suite fast, adding tests to legacy code, knowing when test-first is not worth it, and building a complete feature from an empty file, with every example run before it was printed.