Are you serious? I don't think it would look very good on someone at all if they missed a test date - there would likely have to be a much better reason than they got the dates mixed up. I don't know what the repercussion would be, but I'm sure it's not as simple as booking another date. I would make damn sure I knew when it was and would be well prepared and looking forward to it for a long time before! In fact, I would approach all interactions during the recruiting process as if it were the only chance I had.
I have an interview coming up for a search and rescue volunteer organization, and I have already been told that a no show for the interview without prior notice means there are no more chances to become part of the organization. I can't see the military being much different.