## Best Practices

### DO

- **Follow TDD**: Write tests before code (red-green-refactor)
- **Test one thing**: Each test should verify a single behavior
- **Use descriptive names**: `test_user_login_with_invalid_credentials_fails`
- **Use fixtures**: Eliminate duplication with fixtures
- **Mock external dependencies**: Don't depend on external services
- **Test edge cases**: Empty inputs, None values, boundary conditions
- **Aim for 80%+ coverage**: Focus on critical paths
- **Keep tests fast**: Use marks to separate slow tests

### DON'T

- **Don't test implementation**: Test behavior, not internals
- **Don't use complex conditionals in tests**: Keep tests simple
- **Don't ignore test failures**: All tests must pass
- **Don't test third-party code**: Trust libraries to work
- **Don't share state between tests**: Tests should be independent
- **Don't catch exceptions in tests**: Use `pytest.raises`
- **Don't use print statements**: Use assertions and pytest output
- **Don't write tests that are too brittle**: Avoid over-specific mocks