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tdd

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Use when developing a fix or feature test-first, plan a TDD build, or work red-to-green in slices. Not for hardening: use tests-adversarial. Not for deleting weak tests: use tests-purge-unneeded.

.devin/skills/tdd/SKILL.md

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# Offensive-first TDD

Classic agent TDD rots in a known way: the red test is written as a polite specification, the implementation drifts, and the agent, lacking the metacognition to notice, bends fixtures, weakens assertions, and monkey-patches contracts until green appears. The tokens burn twice and the suite proves nothing. This skill inverts the stance. Red is an attack, not a description: before any implementation, write the tests that try to BREAK the contract, boundary raids, invariant violations, error-path probes, adversarial orderings. Green means the attacks failed to break the code, never that a fixture was satisfied.

## Contract

| Field | Bound contract |
|---|---|
| Trigger | Develop a fix or feature test-first, plan a multi-step TDD build from a spec, or work behaviour red-to-green in slices. |
| Authority | Reversible local: writes only named test and source files; rollback is VCS revert of the implementation commit. No remote mutation. Tests and implementation never change in the same repair step. |
| Side effect | Adds an attack suite and the minimal implementation that survives it, one vertical slice at a time; multi-step work also writes a plan document. |
| Done | Per slice: every contract clause has an attack that failed red for the right reason and passes green unweakened, plus one mutation probe the suite caught. Named evidence: test paths, failing output, passing output, probe output. |

## Inputs