If a fuse is not blown does that mean its completely fine or could it just be getting weak and going bad?

I was told i needed to change the fuses for my o2 sensors on my '02 silverado 1500, but when i pulled them out they were not blown.

Just wondering, haven't hag time to go get new fuses to see if it made a difference.

 

Change them with other fuses with the same amperage rating and see if they work in the other position.

 

Ok thanks for the help.