To test if an item of already worn clothing is suitable to wear out. common amongst students who cant be bothered to do their washing.

the thing that you don’t have when you’re phones percentage is over 20

When you are about to eat pussy, you slowly go down for the alls clear at the belly button. If you can get that far and it doesn't smell bad, you can safely proceed. If there is a stench, you can slowly work yourself back up and shove your dick/or pussy back in her mouth.

When a girl sniffs a guys junk to see if he's been fuckin around with someone else before he came home. If she smells vag, he's guilty as charged.

Similar to definition #1, but instead used to determine whether milk is safe to use. The sniff test is again largely used by students or others that only occasionally go to the shop.