How would you upload a file through mocha/chai for testing?

I'm using the method where the client sends a request to the server to upload a file to an s3 bucket, and then the server sends back a signed request to allow the client to do this. I'm following this tutorial -

http://ift.tt/1pp7jws

Does anyone know how I can write an API endpoint test for this? I'm not doing the client side code since it's an iPhone app but I still want to test my endpoint in my tests.