Best practices for Rails API testing ?

Hello,

I'm developing an API in XML and JSON and I'd to know how you do to test
it.

I thought to create ActiveRessource classes and use them in Cucumber. By
the way, I've a problem with that, I don't know on which port Cucumber
lunch Rails. So I don't know what URL to give to the ActiveRessources
classes.

And you, how do you test your API?

Thank you,
Camille Roux