Unit vs Integration vs End-to-End Tests in a React App

Unit vs Integration vs End-to-End Tests in a React App

There are three main levels of testing in a React app: unit, integration, and end-to-end. Here is the difference and how to balance them.

Unit Tests

Unit tests test a single component or function in isolation. They are fast, numerous, and catch most regressions. RTL tests that render one component and simulate interactions are unit tests.

Integration Tests

Integration tests test how multiple units work together, like a component with a real API mock, or multiple components that interact. They catch bugs that unit tests miss, especially at the boundaries.

End-to-End Tests

E2E tests test the full app through a real browser, simulating real user journeys like logging in and checking out. They are slow and few, but they give the most confidence that the whole app works.

The Test Pyramid

The classic guidance is many unit tests, fewer integration tests, and few E2E tests. Unit tests are cheap and fast; E2E tests are expensive and slow. Balance them accordingly.

The Modern Testing Trophy

A modern view puts more weight on integration tests, which give high confidence at a reasonable cost. The exact mix depends on your app and team.

What to Test at Each Level

Unit: individual components and functions. Integration: components working with their real dependencies, mocked at the boundary. E2E: critical user journeys like signup and checkout.

The Takeaway

Use unit tests for components, integration for boundaries, and E2E for critical user journeys. Balance them by cost and confidence: many unit, fewer integration, few E2E, adapting the mix to your app.