How do I test Express controllers?
Use Jest and supertest. Import the Express app, send requests with supertest, assert on the response. Test happy paths and error paths (validation, not found, conflict). Use a test database so tests do not pollute dev data.
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More FAQs in Writing Clean API Controllers in Express
Parse the request, call a service or model, send the response with the right status code, and handle errors with ApiError. Keep it thin. Move complex logic to a services layer. Use asyncHandler so rejections go to the error handler.
Yes for anything non-trivial. Controllers orchestrate; services do the work. Services are reusable and testable. Without them, controllers become long and hard to test.
Use a serializer (a toUserDTO function) that picks only the safe fields. Never return passwordHash, JWT secrets, or internal IDs. Apply the serializer before sending the response.
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