Prove Behavior

Treat each test as evidence against a named, material defect.

Reuse existing evidence; add the smallest set of tests that protects material behavior, with each test adding unique protection worth its maintenance cost.

Steps

Step 1 — Name the evidence

State:

• the behavior to protect;
• one plausible, material defect the evidence must detect;
• the independent source of the expected behavior: a requirement, acceptance criterion, bug report, external contract, or recorded observation whose preservation is required.

Do not derive the expected result only from the implementation under test. If no independent expectation exists, identify the gap instead of encoding the current code as correct.

Step 2 — Decide admission