Some do. Others take the not unreasonable position that if you competed for those places at a test skate and won them, they're yours unless injury or some other unforeseen event takes you out of the competition, which is an attitude I have to say I prefer.
I have mixed feeling on which is the better approach.
If you skate well at the test skate and then dud out, why not give the spot to a lower placed skater who may have duded out at their test skate and was eagerly awaiting their chance.