Are you testing to make sure there's a dial tone? Or more like a loopback? You can buy a cheap PBX box of some kind, plug it in and make sure you can issue commands to it and that you can hear the response. Folks on here who have worked on these systems may have a better idea..
(If you do a search for Cisco SPA112, that is the relatively cheap box you can buy. Plenty of them, and their cousins, on eBay for cheap cheap cheap)
I also built a circuit from an Electronics Now project that incorporated supplying dial-tone and talk-battery to analog sets from a home PBX type project. It was rife with mistakes and circuit errors though, I did manage to get them figured out and the circuit working.
There are plenty of schematics available from searching Google as well.