Apex test coverage = percentage of Apex code lines exercised by unit tests.
Salesforce requires 75% test coverage before deploying Apex code to production. Reasons:
- Quality gate — untested code is high-risk.
- Bulk-safety — tests exercise bulk patterns.
- Regression — tests catch breaking changes.
Coverage measurement:
- Per Apex class: % of lines hit during test execution.
- Triggers must have at least one test that touches them.
- Test classes themselves don't count toward coverage (they're test code, not production).
Salesforce's coverage rules:
- Production deploy: org-wide coverage 75%+; individual triggers 1%+ (i.e., all triggers must be touched).
- Sandbox deploy: less strict.
Common coverage anti-patterns:
- Coverage tests with no assertions — code lines exercised but behaviour unverified.
- Tests that pass against any change — meaningless.
- `@isTest(SeeAllData=true)` — tests depend on org data, fragile.
Quality vs quantity:
- 75% with assertions — meaningful.
- 75% without assertions — meaningless.
- 85%+ with assertions — strong.
- Test code lines counted — write good tests, not just lines.
Tools:
- Apex Test Execution in Salesforce Setup.
- VS Code Salesforce Extensions — coverage in IDE.
- CI/CD — automated coverage check.
- Apex Code Analyzer — quality + coverage analysis.
Beyond Apex:
- LWC testing with Jest — separate tool, separate coverage.
- Flow testing — limited tools.
- Manual / UAT testing — coverage of features, not just code.
Senior QA insight: 75% is a gate, not a goal. Aim higher. And coverage without assertions is meaningless. Quality of tests matters more than the number.
The senior framing: tests are documentation of expected behavior. Each test asserts: "given X, when Y, then Z." Run tests; behaviour is documented.