I would suggest finding a herding trainer rather than just doing a herding test (unless all you really want to do is watch your dog herd once).
I just started my dog on herding and we do weekly lessons. I don't know what I would do if we were both under the pressure of a full blown show going on and we were being instinct tested.
The other thing you need to find out is how well you react to sheep and ducks. It is a bit intimidating to have 3-4 sheep flocking to you and your dog pushing them around an area. You get knocked around alot at first.
My corgi keeps getting too interested in the sheep poop and stops working the sheep to eat it. She's never had an interest in any poop before! Its so frustrating. My trainer says some dogs just decide they've had enough poop and ignore it from then on.
Watching a corgi herd ducks is so much fun.
Either way, I wish you luck in your herding endeavors
It is a fun sport to get into. If you have any questions I'll share what I know with you.