I recently had to help someone setup an HP fax machine. Previously I would have looked around for someone with a fax machine so I could test out both the sending and the receiving functionality, but as I was reading through the manual I noticed that HP actually has a service that you can use!
You basically send a fax to this number and after five minutes it responds back with another fax to the same number with confirmation that it received the fax. This is a great tool if you ever have to setup a fax machine. Checkout more info on this HP support page.