Testing Strategies
Balancing test coverage, development speed, and confidence in your frontend application.
Quick Navigation: Testing Pyramid • Unit Tests • Integration • E2E • Comparison
The Testing Trade-off
More tests = More confidence but slower development. Finding the right balance is key.
- Coverage vs Speed: 100% coverage slows development
- Unit vs E2E: Different confidence levels and maintenance costs
- Mocking vs Real: Fast tests vs realistic scenarios
Testing Pyramid vs Trophy
Traditional Pyramid
Traditional approach: Many fast unit tests, few slow E2E tests.
Testing Trophy (Kent C. Dodds)
Focus on integration tests for best confidence-to-effort ratio.
Unit Tests
Test individual functions, components, or modules in isolation.
Advantages
- ✓Fast: Milliseconds to run
- ✓Precise: Easy to pinpoint failures
- ✓Cheap: Low maintenance cost
- ✓TDD-friendly: Easy to write first
Disadvantages
- ✗Low confidence: Doesn't test integration
- ✗Mocking overhead: Need to mock dependencies
- ✗False positives: Tests pass but app broken
🎯 Best For:
Pure functions, utility libraries, complex business logic, reducers, custom hooks.
Integration Tests
Test multiple components working together, often with Testing Library.
Advantages
- ✓High confidence: Tests user flows
- ✓Realistic: Tests components together
- ✓Refactor-safe: Less coupled to implementation
- ✓Best ROI: Confidence vs maintenance ratio
Disadvantages
- ✗Slower: More setup, more components
- ✗Harder debugging: Failure could be anywhere
- ✗Mock APIs: Still need to mock external calls
🎯 Best For:
User interactions, form submissions, component composition, feature flows.
End-to-End Tests
Test entire application from user's perspective with Playwright, Cypress, or Selenium.
Advantages
- ✓Highest confidence: Tests real user flows
- ✓Full stack: Tests frontend + backend + DB
- ✓No mocking: Real services and data
- ✓Visual testing: Can catch CSS issues
Disadvantages
- ✗Slow: Minutes to run full suite
- ✗Flaky: Network, timing issues
- ✗Expensive: Infrastructure, maintenance
- ✗Hard debugging: Many layers to investigate
🎯 Best For:
Critical user journeys, checkout flows, authentication, smoke tests before deploy.
Comparison Table
| Aspect | Unit | Integration | E2E |
|---|---|---|---|
| Speed | Very Fast | Medium | Slow |
| Confidence | Low | High | Highest |
| Maintenance | Low | Medium | High |
| Flakiness | Rare | Occasional | Common |
| Tools | Jest, Vitest | Testing Library | Playwright, Cypress |
Best Practices
- 1.Focus on integration tests. Best confidence-to-maintenance ratio.
- 2.Test user behavior. Not implementation details.
- 3.Critical paths get E2E. Checkout, auth, core features.
- 4.Unit test complex logic. Calculations, transformations, utils.
- 5.Mock at network level. MSW for consistent API mocking.