Good point... it would obviously be different on a snooker table with snooker balls which are a different size, diameter, and weight.
I just read about a similar test but you need to judge it by rebound speed. The pool table cushion test says to shoot the ball to the rail. If the rails are brand new the ball will rebound at about one-half the speed at which it was shot. As the cushions age and break down, the rebound speed will decrease.
Here are a few other billiard table cushion testing methods found from around the net:
From a Pennsylvania, PA billiard table service provider:
Test your billiard table cushions by listening very carefully while shooting a ball into each rail. The ball should rebound at a moderate to fast speed AND should make the exact same sounds all around the table on each of the rails. Each table will sound differently based on the design of the rails and frame resonating the energy from the ball striking the rubber cushion. The point is to monitor the consistency all of the way around the pool table. Finally, using pressure from your fingers, you should also be able to squeeze the cushion a distance of between 1/8" and 1/4".
If you know the history of the pool table and how it was treated you can judge by that:
Billiard and snooker table rail cushion rubber should have a life span of 25 to 50 years. This life span can be shortened if the table is misused, exposed to temperature and moisture extremes, or stored improperly. Moisture or extreme cold can cause pool table rail rubber to become either brittle or extremely hard.
Another, we'll call it the "finger cushion test":
Using your fingers, examine the cushions for grooves worn into the cloth underneath the pool table rails where the edges hang over the table's playing surface. These slight tracks, which can be felt with the fingers if you can't see them) are an indication of worn cushions and will cause the rails to be less springy. You will also want to replace the billiard table cloth at this point too.
Another, we'll call it the "top spin cushion test":
With your pool cue elevated roughly thirty degrees from parallel with the floor, shoot a ball into the rail straight ahead, fairly fast, and with moderate top spin. If the ball jumps more than one inch into the air then the cushions may need replacement.
Another, we'll call it the "rebound cushion test:"
You can test billiard table cushion by rolling balls very slowly into the rails. Take notice of how the ball reacts to impact with the rail. Does it come to a rest against the rail (bad) or does it bounce back into the playing area in a lively and springy way (good)? Also, test the rebound angles. Take note of whether the angles of rebound are approximately equal to the angles of incidence (good).