Testing Regression

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