As far as i know cumulative degradation occurs in a MOV when multiple surges appears in a circuit, A way to minimize this degradation is having multiple MOVs in parallel. This kind of damage can be internal and so not detectable by visual inspection.
In this situation i can use a digital multimeter to test the MOV for a short circuit between its terminals. I'm aware that this test is not 100% precise since a MOV can be damaged and present a open circuit between its terminals.
Taking MOV above its breakdown with a high voltage, to see if it conducts and check the clamp voltage does not seems very safe or practical.
My question is:
Beyond looking for short circuits between the terminals with a multimeter is there any practical way of testing a MOV (with no physical damage visible) in a PCB?