testing-checklistlisted

# Testing Checklist A pragmatic checklist for writing and reviewing tests. Read the relevant section for the change at hand rather than the whole file. Tests are the executable spec — optimize them for reading, not for coverage numbers. ## Rationalizations (read first) | Rationalization | Rebuttal | |---|---| | "I'll add tests later." | Later is the load-bearing word — it rarely arrives. The test is part of the change, not a follow-up. | | "Tests pass, ship it." | Passing tests are evidence, not proof. They only cover what they assert — check what they *don't* cover. | | "This code is too simple to break." | Simple code with branch logic breaks at the boundaries. Test the boundaries, skip the trivial middle. | | "Coverage is at N%, we're good." | Coverage measures execution, not assertion. A test with no meaningful assert inflates N and catches nothing. | | "The bug is fixed, no test needed." | A fix without a regression test is a bug on a return ticket. Red first, then green. | | "I'll write the code first, then add tests." | Test-after validates the code you happened to write, not the behavior you wanted. Red first keeps the test honest. | | "I'll DRY up these tests with helpers." | Test code is spec, not production code. DAMP wins: some duplication beats indirection the reader must unfold. | ## What to test (in priority order) - [ ] **Branch logic** — every non-trivial `if`/`switch`/early-return path, especially error paths. - [ ] **Boundaries** — empty input, one ite