msw

Use setupServer from the msw/node entrypoint with your shared handlers, then configure lifecycle hooks in test setup: server.listen() in beforeAll, server.resetHandlers() in afterEach, and server.close() in afterAll. Node.js 18 or higher is required.

Use graphql.query or graphql.mutation handlers matched by operation name rather than URL, since all GraphQL requests share one endpoint. Access variables via the resolver's variables property and return errors in the standard errors array format with status 200.

Common causes include relative URLs in Node.js environments, wrong handler ordering where general handlers shadow specific ones, and unset environment variables in handler URLs. Use absolute URLs or wildcards like */api/user and order handlers from specific to general.

No, MSW v2 does not auto-parse request bodies based on Content-Type. You must explicitly call request.json(), request.text(), request.formData(), or request.arrayBuffer() inside the resolver to access body content.

Define happy-path handlers as your baseline, then use server.use() inside individual tests to override specific endpoints with error responses such as status 401, 500, or HttpResponse.error() for network failures. Reset handlers after each test to avoid pollution.

MSW is not needed for unit tests of pure business logic without network calls, and fully mocked environments should avoid bypass() passthrough to real APIs. Projects still on MSW v1 must use the older res(ctx) syntax until migrating.