Msw V2

MSW is the standard API mocking approach for modern JavaScript testing. Unlike older mock libraries that patch fetch or axios directly, MSW intercepts at the Service Worker level in browsers and via Node.js interceptors, providing realistic mocking without modifying application code. Confidence is docs-derived.

The API surface covers http handlers (http.get, http.post, etc.) and graphql handlers, server.use() for test-specific overrides, and worker setup for browser or Node.js environments. The handler pattern closely mirrors the actual API server pattern.

MSW is a local testing library with no platform auth. No external services. The Service Worker file (mockServiceWorker.js) is placed in the public directory but is only active during development/test.

Operationally, MSW handlers can delay responses, return errors, and inspect request bodies -- enabling comprehensive network scenario testing. The setup is standardized across the testing community. Integration with Vitest and Jest is straightforward.

Documentation at mswjs.io is excellent. The migration guide from v1 to v2 is thorough. Developer experience is outstanding -- MSW has set the standard for realistic API mocking and is actively recommended by React Testing Library maintainers.