A balanced testing strategy catches bugs efficiently. Here's how to structure your tests at each level.
Testing Pyramid#
/\
/ \ E2E Tests (few)
/----\ - Critical user journeys
/ \ - Slow, expensive
/--------\
/ \ Integration Tests (some)
/ \ - Component interactions
/--------------\- API endpoints
/ \
/------------------\ Unit Tests (many)
- Fast, isolated
- Business logic
Unit Tests#
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Integration Tests#
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End-to-End Tests#
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Test Data Management#
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When to Use Each#
Unit Tests:
✓ Business logic
✓ Utility functions
✓ Data transformations
✓ Edge cases
✓ Fast feedback
Integration Tests:
✓ Database operations
✓ API endpoints
✓ Service interactions
✓ External API integrations
✓ Error handling across layers
E2E Tests:
✓ Critical user journeys
✓ Multi-page flows
✓ Authentication flows
✓ Payment processes
✓ Cross-browser testing
Test Organization#
src/
├── components/
│ ├── Button.tsx
│ └── Button.test.tsx # Unit tests
├── services/
│ ├── UserService.ts
│ └── UserService.test.ts
├── api/
│ ├── users.ts
│ └── __tests__/
│ └── users.integration.test.ts
tests/
├── e2e/
│ ├── auth.spec.ts
│ └── checkout.spec.ts
├── fixtures/
│ └── users.json
└── utils/
└── test-helpers.ts
Best Practices#
General:
✓ Test behavior, not implementation
✓ Keep tests independent
✓ Use descriptive names
✓ Follow AAA pattern (Arrange, Act, Assert)
Unit Tests:
✓ Fast execution
✓ No external dependencies
✓ Mock at boundaries
✓ High coverage of logic
Integration Tests:
✓ Use test database
✓ Clean up between tests
✓ Test real interactions
✓ Cover error paths
E2E Tests:
✓ Focus on critical paths
✓ Use stable selectors
✓ Handle async properly
✓ Run in CI/CD
Conclusion#
A balanced testing strategy uses many unit tests for fast feedback, integration tests for component interactions, and targeted E2E tests for critical flows. Each level catches different bugs—invest in the right mix for your application's needs.