JK,
Fluid dampers can be checked to ensure that they are working as they should.
It requires a special piece of equipment, looks like an electronic set of scales. The damper unit is sat face down on the tester, a switch is pressed which activates the tester which puts a vibration at a set frequency into the damper, the test unit then tells you if the damper is operating by the way the damper has controlled the vibration.

We used to have fluid dampers tested this way when rebuilding engines fitted with fluid dampers to ensure we didn't get any comebacks (broken crankshafts) due to faulty dampers.
The only dampers that tested faulty generally had external damage (dings and dents) which usually restricted the free movement of the internal damper ring.

Jim