Untested code is merely confident code.
Confidence is a feeling; tests are repeatable evidence about behavior.
Interpretation
Code can look obvious and still fail at boundaries, under concurrency, or when requirements shift. Tests turn assumptions into executable examples and let the next change challenge them quickly. They do not make software correct, but they make confidence inspectable instead of personal.
Practice
- Test observable behavior and important boundaries.
- Add a regression test with every defect fix.
- Keep tests readable enough to serve as examples.
Anti-pattern
Approving risky logic because an experienced author says it is obvious.