Can I test an API call originated at the server level?

This might be a very dumb question, but I'm going to try.

I have a React app with an API that can be access to the frontend, imagine this:

/api/quotes/1

That endpoint sends another request to an external API and retrieves a quote with the ID 1.

I'm interested in testing the request from the server-side API call (method, params used etc). I'm using Jest for this project, but I'm not sure how to tackle this one. If you have a past example, or documentation, it's going to be more than appreciated. :)