I have a friend who had it done a couple of weeks ago. She has residual short-term memory loss from a car wreck two years ago. Anyway, she said it was like taking the SAT, only kicked up a few notches. I understood it was all written and oral questioning, nothing invasive. She said she was exhausted afterwards, though. She said her brain hurt from thinking hard for so long. But that was the point - to push her to see what she was capable of.
Good luck with yours - I don't know if it will be different for you, since they were testing her memory capability, but I think it will still be some intensive questions (standardized testing type questions).