If you're not sure whether your cloves are still good, there are a few things you can do to test them. First, take a look at the color of the clove. If it's brown or black, it's probably bad. Second, smell the clove. If it doesn't have a strong, pungent aroma, it's probably not good anymore. Third, try tasting a small piece of the clove. If it's bitter or bland, toss it out.
Generally speaking, cloves should be used within 6-8 months of being purchased for best flavor. However, if they're stored properly - in a cool, dark place - they can last up to a year.