What problem does it solve? Bug fixes often ship without a test that proves the defect existed, or with tests that mirror the implementation instead of the public behavior. This Skill guides the creation of a minimal regression test derived from an established reproduction, so the test fails on the affected version and passes after the fix. ## Core Features & Use Cases - Behavior-Driven Assertions: Derives assertions from the public behavior a caller needs, not from the proposed implementation, avoiding tests that mirror internal logic. - Baseline Verification: Instructs running the test against the affected implementation (or an isolated pre-fix checkout) and interpreting failures, distinguishing real behavioral evidence from import errors, timeouts, or collection failures. - Working Tree Safety: Preserves the user's current checkout and uncommitted work, using isolated checkouts instead of reverting the working tree to get a red test. - Use Case: After reproducing a slug-generation bug where punctuation is mishandled, use this Skill to write a small deterministic test asserting the expected punctuation and whitespace behavior, confirm it fails on the pre-fix version, and report the baseline and fixed-version results. ## Quick Start Ask the AI to write a regression test from the existing bug reproduction, verify it fails on the affected version, and report the baseline and fixed-version results.
