Mocking Strategies to Enable Integration Testing Before API Development with MSW

This article addresses the challenges of integration testing in Front-End development when backend APIs are incomplete or do not return specific data, by using MSW (Mock Service Worker). MSW intercepts actual network requests and returns configured mock data, enabling tests to be conducted in parallel with backend development.

Core Features of MSW Usage

• Basic Data Mocking: Configure handlers.ts and server.ts to predefine response data for specific API paths (e.g., /search).
• Runtime Dynamic Modification: Use server.use() to dynamically modify response data (e.g., rect vs rounded types) for each test case to verify conditional rendering.
• Edge Cases and Error Handling: Simulate empty list responses or HTTP error codes such as 404 and 403 to confirm that fallback UIs or error handling logic function correctly.

Scope and Benefits

MSW can be integrated with Jest and Storybook for visual testing or unit testing, and a service worker can be installed on the development server to test in an environment similar to a real browser. This allows for quick consistency checks when API specifications change and improves maintainability.