Verification Discipline

The Principle

Unit tests verify that code-as-written behaves as-written. Smoke and integration tests verify that the system achieves the intended outcome. Those are different questions. You need both.

"All unit tests pass" is necessary. It is rarely sufficient. A finding from the field: four consecutive integration-blocking bugs, all of which passed unit tests, all of which would have been caught by a five-minute smoke test on a fresh environment. The bugs were not exotic — they were the cost of declaring "done" too early.

The Four Failure Modes