Verification principle. Call the code the way its users do and assert the result they observe against a literal expected value.
Applies when you write, change, or keep a test. It ships with the sharpest falsifiable test-quality heuristic in the wiki: if the test would still pass when every imported function returns undefined, rewrite the assertion or delete the test. That single check is what pstack-tdd and pstack-typescript-best-practices both defer to.
See Also
- pstack-poteto-mode — indexes this principle inline and reads the index at task start.
- pstack — the twenty-three-principle set this belongs to.