Backup PFsense router. How to test without Internet?

[unregistered00]

I'm setting up a new pfsense machine as a spare because we're in dire need of it just in case our current pfsense standalone  (with old and phased-out parts) machine dies. However, I don't have a spare network connections that I can use. Is there a way to simulate a working router without the use of an Internet?

What I currently have is a switch, a hub, and a pile of working computers, and a computer to be used for pfsense.

Is the WAN's isp address being saved by pfsense? Would the LAN's mac address cause problems in the if I connect this test machine on a real-world environment (3x 24 port router + 2 internet connections + 60+ computers)?