Testing fuses is somewhat pointless. You'll know how that particular fuse operated, but you'll still have to rely on the manufacturer's curves for the one you replace it with.
What type of fuse? Some age more gracefully than others, and the environment does make a difference. For some a moist environment doesn't matter, for others it will totally mess up the fuse. What's your load profile like? A fuse that stays comfortably warm all the time will far out last one that thermal cycles on a regular basis. Any time you're thermal cycling electrical equipment of any type that can breath at all you're running a water pump, moving water into the equipment. Small amount, slowly accumulated, perhaps, but water none the less.
I’ll see your silver lining and raise you two black clouds. - Protection Operations