Tests

Selection

Add tests or recommend more coverage only for concrete gaps in required behavior or material failure protection. Require the additional protection to justify maintenance and execution cost.
Stop adding cases when they repeat existing protection; retain cases for distinct rules, boundaries, and failure modes.
Choose a test scope that can expose the relevant failure. Exercise real component interactions when correctness depends on their integration.
Treat coverage as evidence of execution, not assertion quality. Test counts, missing test files, and uncovered lines alone do not justify additional tests.

Derive expected results from requirements, contracts, or independently established examples.
Do not use the implementation under test to generate its own expected results or duplicate its logic in the test.
Distinguish tests that preserve observed behavior from tests that establish required behavior.
Assert outcomes precisely enough to reject plausible incorrect results; successful execution alone is insufficient.