Unit Testing Framework

This walks Claude through writing proper unit tests with the AAA pattern across Jest, pytest, JUnit, and RSpec. You get concrete examples for each language, guidance on mocking and test doubles, and patterns for async code and edge cases. The best practices section is solid on fundamentals like testing one thing per test and keeping tests fast. Most useful when you're setting up testing standards for a project or need Claude to generate comprehensive test suites rather than quick validation code. The reference guides cover the specifics you'd actually need to implement TDD properly instead of just checking if something doesn't crash.