Former Heavyweight Champion, Joe Frazier, once said that butterflies/jitters is only natural... and in fact, he didn't know any fighter of his caliber, who did NOT get them before a fight.
If a Heavyweight Champion boxer says 'it's normal'... you can believe it's normal for a student going up to test for their next rank also.
I used to get butterflies as we got within a few blocks of emergencies in the fire department.
Best way to handle the butterflies... is just to get your mind on business. Don't second guess yourself...
1.) Remind yourself that you've trained in what you need to, and trained correctly, and are therefore READY to test.
2.) Remember that your JOB, is only to go up when called, and DO what you TRAINED to do.
3.) Remember that NO MATTER WHAT HAPPENS... you're doing something that a lot of people don't even have the guts or interest to TRY to do... (So you're a step ahead of most people, for just showing up to try)
4.) Remember that the WORST that can happen... is that you do not promote this go around, and you WILL be FREE to TRY AGAIN if that happens. (So no matter what happens, the world's not going to end!)
5.) Remember your instructor probably wouldn't let you test, if you were not ready in their opinion... and THEY are the ones who decide whether or not you pass... SO... just getting their permission to test, is a good indicator THEY think you're ready.
6.) All you have to do is what you trained to do... and you DID train to do it. So... there's nothing to 'worry' about.
Think about the things you must do to pass... (and you should know what those things are, since your instructor has made you practice them prior to giving you permission to test) Go through them in your head... imagine yourselve going in there, and just doing what you're trained to do, and doing it right.
Then... when the time comes... and they call your name... just do your job to the best of your ability... and let the chips fall where they may.
For what it's worth, some 20 plus years after my very first martial arts testing... I 'still' get butterflies when I'm waiting to test.;)
The past is done... The future doesn't exist yet... only the present exists... so don't worry about anything but doing what you trained to do... and you'll do fine.;) Get used to the 'butterflies'... they're normal... don't dwell on them...
Keep kicking!:)