There are two that I use;
One has a handle that has maybe 18" of leverage on the shock. It is mostly used for checking the damper alone, not for a shock that is aired up.
The other one has a longer handle, maybe 28-36" of leverage on the shock. This one is mainly used for equalizing the positive/negative air chambers on shocks without a bike. But it could work for testing a fully aired shock.
I think mostly you look at testing the damper alone, and test the fully aired shock on a bike.
The shock mounts can be super simple. You don't need to capture each end, the bottom can just rest on a piece of wood or plastic. The top mount can just be a simple 1/2" bolt that passes through the eyelet (with hardware removed). All shocks have a 12.7mm diameter hole in the eyelet, so a 1/2" bolt is perfect.
For trunnion shocks, Fox makes a nice tool that you can use with a dyno as well as to work on the shocks;
View attachment 1969234
Here is a very nice dyno to use for design inspiration;
One dyno to do ALL shocks!!! (well, mostly) No extra Kit needed! Key improvements: 100mm longer dyno handle 30mm taller dyno tower Combined mounting parts so ordering a KIT is NOT necessary for this ‘20 Dyno Added 10mm pin Diagnose rear shock issues with this key fixture—a must