You can test the Air Admittance Valve in several ways:

1. You can take off the AAV and cap the pipe off and see if the smells are still apparent.

2. You can push the opening of the AAV in a bucket of water and see if it traps a pocket of air. You should feel some resistance against your hand. If it does, the AAV is working properly. 

If the valve does not trap air and you are able to push the valve fully into the water without any resistance, the valve is not working correctly and will need to replaced.