tdd-red-green-refactor

One-line summary

The TDD cycle: write a failing test (red), write the minimum code to pass it (green), refactor while staying green. Repeat one tiny step at a time. The discipline is in the order and the minimum — both are easy to skip.

When to use this skill

• Building new behavior in code where you can articulate the desired outcome as a test.
• Bug fixing — write the regression test first (see tdd-regression-test), then fix.
• Designing an API from the consumer's side — the first test forces you to consider what calling code wants.
• Working in a codebase with a healthy test suite where TDD adds little friction.

When NOT to use this skill

• Pure exploration / spike work where you don't yet know the shape of what you're building. Spike first, then test-drive the rewrite.
• Throwaway scripts, one-shot utilities, or rapid prototyping that won't be maintained.
• UI tweaks where the cycle of "write a test, change a pixel, see the test pass" is more pain than benefit.
• Codebases with no existing test infrastructure where setting up the harness for one feature is disproportionate. Add tests; don't pretend you're doing TDD if you can't.

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