Regression Testing

Run regression tests to ensure new changes don't break existing functionality, coordinating with other test types for comprehensive coverage.

When to use me

Use this skill when:

• Making code changes that might affect existing functionality
• Preparing for releases or deployments
• Running automated test suites in CI/CD pipelines
• Validating fixes don't introduce new bugs
• Ensuring backward compatibility

What I do

• Coordinate with other test types:

  • Run unit tests to verify individual components still work
  • Execute integration tests to check component interactions
  • Perform end-to-end tests for critical user workflows
  • Check API contracts remain unchanged

• Test selection strategies:

  • Run all tests for major changes
  • Selective testing based on change impact analysis
  • Risk-based regression testing for high-impact areas
  • Automated test suite prioritization

• Integration with development workflow:

  • Pre-commit regression testing
  • Pull request validation
  • Release candidate testing
  • Hotfix verification

Examples

# Run full regression suite
npm run test:regression           # Full regression suite
npm run test:regression:quick     # Quick regression (smoke tests)
npm run test:regression:selective # Tests related to changed files

# CI/CD integration
npm run test:ci                   # CI regression suite
npm run test:pr                   # PR validation tests

# Test selection based on changes
npx jest --listTests | grep -E "(auth|user)"  # Select auth-related tests
npm run test:affected -- --base=main          # Run tests for changed code

# Coordinate with other test types
npm run test:unit && npm run test:integration && npm run test:e2e:critical

Output format

Regression Test Results:
──────────────────────────────
Test Scope: Selective regression (changed: auth module)
Execution Order:
  1. Unit Tests (auth service): ✅ 42/42 passed
  2. Integration Tests (auth API): ✅ 8/8 passed  
  3. E2E Tests (login flow): ✅ 3/3 passed
  4. API Contract Tests: ✅ No breaking changes

Dependencies Verified:
  - User service depends on auth: ✅ No issues
  - Session management: ✅ Compatible
  - Third-party auth providers: ✅ Still functional

Impact Assessment:
  - High Risk Areas: 0 affected
  - Medium Risk Areas: 1 (password reset flow)
  - Low Risk Areas: 3

Recommendation:
  - All regression tests pass
  - Safe to merge/deploy
  - Monitor password reset in staging

Notes

• Regression tests should be fast and reliable
• Automate regression testing in CI/CD pipelines
• Use test suites that other test types (unit, integration, e2e) have validated
• Implement flaky test detection and quarantine
• Consider visual regression testing for UI changes
• Track test execution time and optimize slow tests
• Use parallel execution where possible
• Maintain test data consistency across runs