Glossary
By the Glue Team
Code coverage is the percentage of code executed by automated tests. It measures what tests are checking. 100% coverage means tests exercise every line of code. 0% coverage means no tests. Coverage is useful but not sufficient—bad tests can achieve high coverage.
Code coverage includes:
Risk Reduction: Uncovered code is untested. It's where bugs hide. Coverage shows what's at risk.
Change Confidence: If code is well-covered, you can refactor confidently. Changes fail fast in tests.
Regression Prevention: Tests catch regressions. Untested code regresses silently.
Quality Indicator: High coverage (with good tests) correlates with quality. Low coverage indicates risk.
"100% coverage means no bugs." False. Bad tests can achieve high coverage. 70% coverage with good tests is better than 100% with pointless tests.
"Coverage is the only quality metric." False. Code review, architecture, testing practices matter too.
"We should achieve 100% coverage." False. Target 70-80% on critical paths. Some code doesn't need testing (getters, trivial code).
Testing: Coverage measures testing effectiveness.
Code Health: Coverage is one dimension.
Technical Debt: Untested code is debt.
Q: What's a good coverage target? A: 70%+ on critical code is good. 50-70% is acceptable. 0-50% indicates risk.
Q: Should you add tests to existing code? A: Add tests for changed code. Incrementally improve coverage for high-risk code.
Q: How do you improve coverage? A: Write tests for untested paths. Focus on error cases and edge cases first.
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