First of; you can actually test it manually by taking off your shocks out of the car. 'You'll be needing spring compressor to do this'. Then try to squeeze the shaft against the body; by doing that, you can able to assess if there is less or enough resistance in movement of the shaft along with the force you applied. If there is less resistance or 'no' resistance at all, your shock is 'shot'.. You've got to change it..