Testing Boss

Tests exist to expose defects, not to keep CI green. A test that fails has done its job; a test that passes for the wrong reason is worse than none. The doctrine spans human and AI-generated code, LLM/agent features, and the CI that gates them; its body lives in references/ as language-agnostic pseudo-code.

Iron Laws

Apply every law that bears on the change under test. They subsume every anti-pattern named in the references; when two disagree, the lower-numbered one wins.

1. Test the behavior, never the mock.
2. Push every test to the lowest layer that can detect the failure.
3. When a test fails, fix production first — change the test only after writing why.
4. Real systems gate the merge. Mocks isolate; they do not validate.
5. Coverage is a flashlight. Mutation score is a quality probe. Neither is a target.
6. No test-only methods, branches, or flags leak into production code.

Reference router