Hi Kriston,
I'm so excited for you! I think it's great that you have gotten to this part of the journey.

It's quite normal to be nervous. Unfortunatly, I believe that it's best to shield your child from these feelings, which is almost impossible, but you are well on your way be talking to us. I would also reccomend that you journal on your own experience of being "identified." If your child is as emotionally perceptive as mine is, you will need to give him a brief verbal statement that is true, but as undramatic as possible. Practice what seems to fit you, or if I'm close, steal this:

Mom: Remember that old test you took last time?
ds: yes
Mom: Did you like doing it?
ds: oh, yes!
Mom: You know that DH and I are responsible for teaching you or finding places where you can learn, what's your job?
ds: ((results will vary))
Mom: I take my responsibility very serious don't it?
ds: ((child will usually agree and laugh))
Mom: It's always good to have help for important jobs, right?
ds: (( results will vary, but I imagine a big smile of agreement here))
Mom: And that's why I'm so excited about the new test at Dr. X's. After the test she'll be ready to help me do my responsibility to you! Yippee!

Then the trick is not to bring it up again with DS - HA! This isn't easy, but it think it's worth trying.

Other tips:
pack healthy food,
make a packing list with DS as a homeschool task,
bring favorite cuddly,
Plan travel route with DS as a homeschool task.
Keep bedtimes consistient.
Get outside each day for the next few days.
Arrive early, even a day early to acclimate.
Plan a fun activity, or swim at the hotel before the test.

Best wishes,
Trinity