test-driven-development

Test-driven development enforces writing a failing test first, then implementing minimal code to pass it, then refactoring safely. This Skill guides you through the RED-GREEN-REFACTOR cycle using pytest for Python or cargo test for Rust, ensuring disciplined development and preventing shortcuts that lead to regressions.

The RED-GREEN-REFACTOR cycle is a TDD workflow: write a failing test (RED), implement minimal code to pass it (GREEN), then improve code quality without breaking tests (REFACTOR). This approach reduces bugs, improves code quality, and ensures every line of code has test coverage before it ships.

Refactoring safely requires running all tests after every change to catch regressions immediately. This Skill enforces running single tests for immediate feedback during development and comprehensive test suites before refactoring, protecting code integrity throughout the improvement process.

Yes. This Skill provides language-specific test workflow guidance for both Python pytest and Rust cargo test, enforcing the same RED-GREEN-REFACTOR discipline and test isolation practices across different project types while guiding you through writing tests and updating SPEC markers.

Running a single test gives immediate feedback while developing a feature; running all tests catches regressions across the entire codebase. This Skill guides you to use single tests for rapid iteration and comprehensive test runs before refactoring to ensure no existing functionality breaks.

Writing tests first clarifies what code should do before you write it, prevents over-engineering, and guarantees test coverage from day one. Test-driven development reduces the likelihood of untested edge cases and makes refactoring safer because you know immediately if changes break intended behavior.