The test measures how much saliva you produce after consuming a drop of lemon juice.
and some friends
You may think to yourself, how the hell does this measure introversion/extroversion? The Reticular Activating System in your brain reacts to certain stimuli such as food or social encounters. Introverts have a high level of activation which in turn means that they will produce more saliva. Extroverts have a lower level of activation, thus less saliva. If you are interested in comparing yourself to your friends, check out the following link.
What does it all mean? Basically, introverts are more reactive towards stimuli in the environment. Just the opposite is true for extroverts. Introverts are perfectly satisfied with little excitement and few people around to enjoy that excitement. Extroverts need a little more action to keep their interest.
I am a bit more introverted than I ever really considered myself to be over the last few years. I am outgoing and I enjoy meeting new people, but I prefer those close intimate conversations with just a few people. The introvert is not the most popular guy in the crowd, but the extreme extrovert can be a bit over the top. Introvert are not simply shy, they just get enough excitement in small doses. Extroverts are not simply outgoing, they just need a bit more excitement in their lives to feel alive.
The introvert is not a loser, nor is that person particularly lonely. The extrovert is not aloof or careless of what others think. Our minds are different and unique, that is what makes humanity so colorful. Consider yourself, consider others, and just be considerate.