Why are the url parameters to an api parsed correctly by this lib but not by others?

[riha]

I'm new to Next.js and I have previously tested my API endpoint using supertest. That worked fine until I tried to get the parsed URL parameters in an API - just keep getting undefined in the parameters property of the request in the API handler. So (in for example and API route /api/test/[id] the id when requesting /api/test/33 33 won't be parsed out to the parameters object in the API handler).

Same happened then using next-test-api-route-handler until I specifically set the params object in testApiHandler. Then it worked 😅

I'm just trying to understand what's actually going on. What's different from calling the API in a test from actually doing the request from the frontend? Is there some middleware in next that isn't run when running the test?

[Xunnamius]

Your instincts are correct that Next.js is invoking some dynamic parameter parsing "middleware" somewhere else that is not invoked when just running the API resolver function in isolation, and certainly not when emulating Next.js routing via a request testing library (supertest, node-mocks-http, etc). In fact, Next.js's API resolver function uses dependency injection to get its URL parameters object, which NTARH takes full advantage of to inject the params object during testing. This is why setting params in NTARH just works 🙂.

This answer might shed more light on things too.