name: tdd description: Test-driven development with red-green-refactor loop. Use when user wants to build features or fix bugs using TDD, mentions "red-green-refactor", wants test-first development, or requests TDD workflow.

Test-Driven Development

Philosophy

Tests verify behavior through public interfaces, not implementation. Good tests survive refactors.

See principles.md for testing philosophy and anti-patterns.

Workflow

1. Planning

•Confirm interface design with user
•List behaviors to test (prioritize critical paths)
•Get approval before writing code

2. Tracer Bullet

code

RED:   Write first test → fails
GREEN: Minimal code to pass → passes

3. Incremental Loop

For each remaining behavior:

code

RED:   Write next test → fails
GREEN: Minimal code to pass → passes

Rules:

•One test at a time
•Minimal code to pass
•No refactoring while RED

4. Refactor

Once all tests GREEN:

•Remove duplication
•Improve structure
•Tests must stay GREEN

Anti-Pattern: Horizontal Slices

DO NOT write all tests first, then all implementation. DO use vertical slices: one test → one implementation → repeat.

See examples.md for workflow demonstrations.