Skill: TDD (Strict)

Rule

Every code change follows the full red/green/refactor loop. No exceptions. This applies each time new functionality is written or existing behavior is changed, regardless of how far into a session we are.

The Loop

1. Red — Write a failing test first

• Write the test before any implementation exists
• Run the test and confirm it fails with a meaningful error
• A test that passes before implementation is wrong — delete it and write a better one
• Do not proceed to Green until you have seen a red failure

2. Green — Minimal implementation

• Write the minimum code required to make the test pass
• Nothing more — no extra features, no speculative code
• Run the test and confirm it is green

3. Refactor — Clean up

• Improve structure, naming, duplication while keeping tests green
• Re-run tests after every refactor change
• Do not add new behavior during refactor

4. Commit

• Commit after each green/refactor cycle
• Commit message should reflect the behavior added, not the mechanics

Failure Modes to Avoid

Resuming Mid-Session

If TDD discipline has slipped during the session:

1. Stop current work
2. Identify what implementation exists without a corresponding failing test
3. Write the missing test(s), confirm they pass (they should, since implementation exists)
4. Note: you cannot go back to red for existing code, but document the gap and continue strict TDD from this point forward

Checkpoint Format

After each cycle, note:

Red: <test name> failed with <error>
Green: <what was implemented>
Refactor: <what was cleaned up, or "none">
Committed: <short sha>