Well, you can stop swapping them when the circuit starts working :)

If you're talking about the fuses that have a base like a regular lightbulb, there's often a little window that you can look in and see if the part that "blows" is still intact or not.

Cartridge fuses are a bit harder.

But you can remove the fuse, test it with an ohmmeter, and put it back if it reads zero ohms (it doesn't need replacing then).