testing

How to WRITE real, maintainable tests in any stack — assertions that fail when the code is broken, the test pyramid and AAA structure, behavior-over-implementation, mocking discipline, fixtures, coverage that means something, and the ship gates (test-count-never-decrease, no self-mocking, prove-RED-first). Language-generic with concrete examples in TypeScript/JavaScript, Python, Rust, and Go. Use when asked to "add tests", "write a test", "improve coverage", "fix a flaky test", "how do I test X", when turning a hollow assertion into a real one, deciding what layer a test belongs in, or when a change must not drop test quality. The construction counterpart to the crucible-detective agent's fraud hunt.