Introduction

Python’s testing tools are lightweight enough that it’s easy to write a lot of tests without writing good ones. A suite that mocks every collaborator, duplicates the same assertion ten times with different inputs pasted in by hand, or chases a coverage number will pass in CI and still miss real bugs.

pytest gives you fixtures, parametrize, and monkeypatch — the tools that make it just as easy to write the right tests as the wrong ones. This post covers how to use them well.