Mutation Testing
// Definition
Measuring test quality by deliberately introducing small bugs (mutations) into the source and checking whether tests catch them. A high mutation score means the suite genuinely exercises the code, not just executes it. More honest than line coverage.
// Related terms
Code Coverage
The percentage of source-code lines, branches, or statements executed during a test run. A useful but easy-to-game metric — high coverage doesn't guarantee good tests.
Test Coverage
A measure of which parts of the requirements or features have been exercised by tests. Distinct from code coverage — focuses on the spec, not the source.
TDD (Test-Driven Development)
Write a failing test first, write the minimum code to make it pass, refactor. Drives design through tests rather than testing afterward — and produces a thorough unit test suite as a byproduct.