test-strategy

# test-strategy Coverage % is a number with no method. This skill makes the QA plan defensible: **what** to test, **why** that set, and a **real** signal that the tests bite. qa-engineer emits `docs/qa-reports/TEST-STRATEGY-{slug}.md` capturing the four decisions below; the QA gate checks the file exists for medium/large features. ## 1. Pyramid ratio — pick by archetype (not by reflex) The right unit:integration:e2e mix depends on where the risk lives. | Archetype | unit | integration | e2e | why | |-----------|------|-------------|-----|-----| | library / devtools / cli | 80% | 15% | 5% | logic-dense, few I/O seams | | web-app / saas | 60% | 30% | 10% | request→db→render seams dominate | | commerce / fintech / marketplace | 50% | 35% | 15% | money paths need cross-component proof | | data-platform / streaming | 45% | 45% | 10% | correctness lives in pipelines, not units | | ai-system / agent-product | 50% | 20% | 10% + **evals 20%** | behaviour is the contract → eval set (see [[decision-eval]]) | State the chosen ratio in TEST-STRATEGY and justify any deviation. ## 2. Case selection — equivalence / boundary / property Don't enumerate inputs; **partition** them. - **Equivalence classes** — one representative per class of behaviour (valid, invalid, empty, max). Testing 5 valid ids ≠ testing 5 classes. - **Boundaries** — the bug lives at the edge: 0, 1, n-1, n, n+1, off-by-one, empty, overflow, the threshold itself. - **Property-based** — for pure/transform logic, asser...