test-disciplinelisted

<!-- Generated by `basicly skills-build` from skill.yaml. Do not edit; edit the source. --> # Test Discipline Keep a test suite trustworthy as it grows. These are judgment rules, not lint — the deterministic floor (formatters, type checkers, the test runner itself) cannot catch a test that passes today but lies. Apply them when authoring or reviewing any automated test, in any language. ## Isolation and ownership - A test owns its inputs. Build the fixtures it needs and tear them down; never read or assert on state that another test, a previous run, or the developer's machine happened to leave behind — a test that reads state it did not create is broken even when it passes today. - A test must pass alone, in any order, and in parallel: no shared mutable state, no reliance on execution order, no hidden dependency on a sibling running first. ## Assert on behavior, not internals - Assert on observable behavior and public contracts — return values, emitted output, externally visible side effects — not private fields, call counts, or internal structure a refactor should be free to change. - A test that breaks on a pure refactor is testing the implementation, not the contract. Prefer the coarsest assertion that still proves the behavior. ## Determinism - Remove nondeterminism at the source: pin the clock, seed randomness, stub the network and the filesystem. A flaky test is a broken test, not a "sometimes" test — fix or quarantine it, never mask it with a