testing

# Testing Discipline <!-- routing-eval reads this line; it lives in the BODY so the always-on skill LISTING stays inside Claude Code's budget (1% of the context window) — an overflowing listing gets descriptions truncated or dropped, which strips the very keywords a match depends on. --> Trigger phrases: "write a test", "run the tests", "coverage", "are the tests green", "unit test", "integration test" Goal: **behavior correctness** — test real behavior without breaking product code just to make a test pass. ## Principles - **Pyramid:** many unit, fewer integration, few end-to-end (e2e). Limit e2e to critical flows. - **AAA:** Arrange-Act-Assert; **one test = one behavior**. - **Isolation & determinism:** external dependencies are mocked/faked; time and randomness are fixed; test order is independent. - **Risk-coverage:** risk, not metrics. Critical path + **boundary** + **negative** + **authorization (IDOR/404)** scenarios. - **Naming:** `what_it_tests_under_which_condition_what_it_expects` — on failure it is clear what broke. - **Red-green:** first a failing test, then the implementation. ## Watch out - **Flaky = bug:** an occasionally failing test is not tolerated; it is fixed at the root. - In snapshot/golden-file tests, avoid needless brittleness (assert only the meaningful output). ## DoD (this skill's contribution) - The project's own test command is green — read it off the manifest/CI (`dotnet test` · `npm test` · `pytest` · `go test ./...`), don't as...