Basic Fuse Question
 

My radio went dark (boo!) so I switched out the fuse, and it's happy again (yay!). But the fuse I removed looks fine. I thought if they blew, the metal strip would be obviously damaged?

Could be a hairline fracture.

Could be you had a bad connection at the fuse box and simply replacing the fuse 'cleaned' the contacts.
Try sticking your old fuse back in. Won't hurt anything.

I don't know how many times I went to do a voltage check on things including cars that merely the probes coming into contact with connections solved the issue. Yes, probably a bad connection.

Test it
 

This is the only way to tell. I had a problem with my E36 years ago.....looked at every fuse in the car....they all looked fine. Finally drug out the VOM and started testing for continuity and found it.....it looked like nothing was wrong with it......but