Learning about payment gateways

[fonzi]

I have been applying for a few web developer jobs but they usually ask for knowledge of payment gateways.I have never worked in a commercial web development company so I don't have that experience (I have only put up ASP.NET websites by myself).
Is there a way I can put a payment system in place on a site without actually using real information (credit card details etc.)
I need to learn about this stuff but it is a bit difficult when you can't apply it to a working example (if you know what I mean).

 

[MOH]

Paypal sandbox is the only one I've used.

I would have though Realex and the like would have something similar, but can't seem to find it.
You may get some useful info from here though.

[edit]
From this thread, it appears you may have to sign an NDA to set access to the Realex API documentation, which seems a bit odd