Testing ISDN Backup ccts

I need to test the availability of ISDN backup circuits.I do not want a backup test merely to check the D channel functionality,we have about 50 backup ccts and have had numerous occasions when these ccts are out of service when called upon to perform.I would like to automate and schedule D channel tests without investing in additional hardware.I do not want to reinvent the wheel – someone must have been down this road before.