Make the broken behavior executable before changing production code: write the focused regression test that fails before the fix and passes after it. Understand the bug, choose the narrowest executable check, write the failing test, run it before fixing to confirm it fails for the intended reason, make the smallest production change, rerun, then run nearby validation.
pstack’s member of the pattern-test-driven-development cluster is the one that argues against itself, and that is what makes it worth a page. Where speckit makes TDD non-negotiable and superpowers auto-triggers sp-test-driven-development as a gate, this skill’s own frontmatter restricts it to cases where the user explicitly asks or the bug has an obvious cheap local test target, and its body opens by telling you when not to use it. A test is skipped when it would need broad harness setup, brittle mocks, slow end-to-end infrastructure, production-only state, vague reproduction steps, or large unrelated fixture churn.
The skipping is not silent. Do not silently skip the regression step — explain before fixing why a failing test is impossible or not worth the cost, then use the closest executable regression check available: a targeted script, a manual reproduction command, browser automation, a snapshot comparison, a log assertion, a focused integration check. The obligation is to executable evidence, not to a test file.
It ships a definition of the thing it is avoiding. A bad test is one that mostly tests mocks, encodes current implementation details, depends on timing or unrelated global state, needs expensive infrastructure for a small fix, or would be deleted immediately after proving the fix. Prefer no new test over a bad test. The companion falsifiable check lives in pstack-principle-test-behavior-not-implementation: if the test would still pass when every imported function returns undefined, rewrite the assertion or delete the test.
Guardrails close it out: do not change tests merely to match a wrong implementation, and do not weaken existing assertions unless the expected behavior has genuinely changed and the reason is clear.
See Also
- pstack-principle-test-behavior-not-implementation — the test-quality rule this defers to.
- pstack-create-verification-skill — the answer when there is no cheap local test path at all.
- mp-tdd · sp-test-driven-development — the TDD cluster; both treat the practice as more nearly mandatory than this does.
- stage-implement — the canonical stage this implements.