How can you test to see if your helmet is bad.?

If it has taken a hit, replace it. Bicycle helmets are designed to take one and only one whack. They work by destroying themselves to absorb the energy that would otherwise scramble your egg. If your helmet is just old, inspect it for structural integrity. Make sure the shell and the liner are still well attached and that the straps are still secure. Verify that the webbing is still in place and secure. If in doubt, get a new one.

HTH

Helmets are good for 2 years. If it has been in a accident than replace it. this is true for any type of helmet.

I agree with above answers, if it's been in an accident at all replace it.

Also you should be able to tell just by looking at it. Compare to a new one.

If the foam isn't smooth any more and if it shows a bunch of small cracks then

it's worn out.