Now don't go saying things like that. No one martial art is truly better then another. It all depends on what works for you. I have tried a handful of different martial arts, each with very different approaches to fighting, and some of them I just had a better natural understanding for. If Tae Kwon Do is something that works for you and you really put your heart into it then you will be as good as someone that puts their heart into Muay Thai or Kung Fu.
It's all about the individual's drive and passion. Martial Arts is a way of life. Those of us that chose this lifestyle should never criticize other styles of martial arts - we can learn a lot from each other. Regardless of style, those that live martial arts should all be allies!
Good luck with your yellow belt test abuja! The only advice I can give you is this: don't spend a lot of time worrying about impressing whomever is testing you - do it for yourself. The only way to prove to your instructor that you are worthy of the next belt level is by first proving it to yourself!