Test-Driven Development

Use before implementing any feature or bug fix.

Iron Rule

No production code without a failing test first.

If you wrote implementation code first, delete it and restart with tests.

Red-Green-Refactor Loop

1. Red

   • Write one failing test for one behavior.
   • Run it and confirm it fails for the expected reason.

2. Green

   • Write minimal code to pass that test only.
   • Run the test and confirm pass.

3. Refactor

   • Improve clarity/duplication while staying green.
   • Re-run tests.

Repeat for the next behavior.

Rules

• One behavior per test.
• Prefer behavior tests over implementation-detail tests.
• Keep mocks minimal and interface-aligned.
• Add regression tests for every bug fix.

Project Verification Commands

Use fast-first loop:

typecheck.sh <file>
bild --test <namespace>

Do not claim success until tests pass after your final code changes.