tdd

Invocation points:

• Task plan calls out behavior with a clear external contract (pure function, API endpoint, module boundary)
• Bug fix — write the failing repro test first, then fix
• Refactor into a new module — write the tests against the new interface first

Do not use this skill for:

• Exploratory spikes (use /gsd start spike — no production code ships)
• Pure UI polish where visual verification beats unit tests
• Scripts that run once and are deleted