Beyond the Numbers: A Pragmatic Approach to Test Coverage

4 min read • Jan 13, 2025

A development team celebrates reaching 90% test coverage, only to find critical bugs in production the next day. Sound familiar? While test coverage is a valuable metric, it’s just one piece of the software quality puzzle. In this article, we’ll explore a pragmatic approach to testing that focuses on value and effectiveness rather than just numbers.

What You’ll Learn

  • Understanding different types of tests and when to use them
  • Strategies for testing frontend, backend, and API code
  • Practical approaches to improve test effectiveness
  • Common testing pitfalls and how to avoid them
  • Tools and frameworks for building a robust test suite

The Testing Pyramid: A Foundation for Quality

Modern software testing follows a pyramidal structure, with unit tests forming a broad base, integration tests in the middle, and end-to-end tests at the top. Let’s explore each layer and understand its role in ensuring software quality.

Unit Tests: The Foundation

Unit tests verify individual components in isolation. They should be:

  • Fast and deterministic
  • Independent of external services
  • Focused on business logic rather than implementation details

Integration Tests: Connecting the Dots

Integration tests verify that components work together correctly. They:

  • Test interactions between multiple units
  • May involve external services or databases
  • Focus on business workflows

End-to-End Tests: The User Perspective

E2E tests verify the entire application stack. While valuable, they should be used judiciously due to their:

  • Higher maintenance cost
  • Longer execution time
  • Greater potential for flakiness

Frontend Testing: Beyond the Click

Frontend testing requires a user-centric approach. Instead of chasing coverage numbers, focus on:

Critical User Paths

Identify and thoroughly test the journeys that matter most to your users:

  • Authentication flows
  • Checkout processes
  • Data entry and validation
  • Error handling and recovery

Component Testing

Test components by:

  • Verifying rendering logic
  • Testing user interactions
  • Checking state management
  • Validating accessibility

API Testing: The Integration Layer

API testing bridges the gap between frontend and backend, focusing on:

Request/Response Validation

  • Verify correct status codes
  • Validate response formats
  • Test error handling
  • Check authentication/authorization

Backend Testing: Building Reliable Systems

Backend testing requires a balanced approach between isolation and integration:

Unit Testing Strategies

  • Use dependency injection for better testability
  • Mock external services appropriately
  • Focus on business logic coverage

Database Testing

  • Use test databases or in-memory alternatives
  • Reset state between tests
  • Test migrations and schema changes

Common Testing Pitfalls

Anti patterns to Avoid

  1. Testing Implementation Details

    • Focus on behavior, not internal methods
    • Avoid excessive mocking
    • Test through public interfaces

  2. Brittle Tests

    • Avoid hard-coded values
    • Use data builders and factories
    • Focus on essential assertions

  3. Poor Test Organization

    • Follow the Arrange-Act-Assert pattern
    • Use descriptive test names
    • Group related tests logically

Tools and Infrastructure

  • Unit Testing: Varies by language (JUnit, pytest, Jest, etc.)
  • E2E Testing: Playwright, Cypress
  • API Testing: Postman, Insomnia, Playwright if you’re already using it for E2E
  • Performance Testing: k6, Apache JMeter

Continuous Integration

  • Run tests on every pull request
  • Maintain separate test suites for quick and full testing
  • Monitor test execution times
  • Track flaky tests

A Pragmatic Approach to Coverage

While coverage is important, focus on these key principles:

  1. Value Over Numbers

    • Prioritize testing critical business logic
    • Focus on user-facing functionality
    • Test error conditions thoroughly

  2. Sustainable Testing

    • Write maintainable tests
    • Avoid duplicate test coverage
    • Regular test suite maintenance

  3. Continuous Improvement

    • Regular test review sessions
    • Update tests with new features
    • Remove obsolete tests

Conclusion

Test coverage is a useful metric but shouldn’t be the sole focus of your testing strategy. By taking a pragmatic approach that emphasizes value, maintainability, and user impact, you can build a more effective test suite that truly supports your development process.

Remember: The goal isn’t to achieve 100% coverage, but to have confidence that your application works correctly for your users.

Happy testing! 🧪🚀

For more insights on this topic, check out the article by Kent C. Dodds on The Practical Test Pyramid .

Kent C. Dodds also has an article that extends on these concepts with The Testing Trophy and Testing Classifications .