There are several manufacturers of these testers.
Vibrac in Amherst NH is probably the best known. They have lab or production systems that can measure motors with a wide range of inertia matching. (expensive but good)
Magtrol has equipment that can do the job.
Also, a company in the Chicago area (S. Himmelstein) has some excellent equipment. I used their modules to build a custom system for a company I was working with in Korea.
Ther are a couple of offshore (Japanese) sources also. These are quite good.
You need to consider;
1. Cost
2. Speed of test
3. Accuracy. Detent can be accomplished with a Torque watch, but will ony give the high readings.
Good luck!