No, Hammer isn’t based on Asterisk, but it’s a mature, industry standard tool that does exactly what you want it to do.
You have to make the decision:
Is your time and effort worth more or less than the cost of obtaining a product like Hammer? And how reliable would you consider the results of an Asterisk based test system?
Proper telecom test systems try to cause a failure to determine another system’s capacity and limitations. But what happens when a failure occurs?
Was it the Asterisk test system that failed? Did you overload the Asterisk system or the system you’re trying to test? Would the Asterisk system have worked if only it wasn’t playing audio files? How would you determine that?
Suppose you figure out that the Asterisk system can’t keep up with the system you’re trying to test; How do you now determine the limits?
If you’re trying to certify a system, I believe that you should go with a supported well documented product. You may find that the effort you put into building a trusted test system from Asterisk is more than you bargained for.
As a testing system, I think that Asterisk may be outside of it’s element. Yes, you can get Asterisk to place calls, play sound files, etc… But…