I apologize for not being of more assistance. That said, while I have grown out of that phase, I would say you have to let it pass. And I do have a brother who is like that sometimes. You can't exactly force him to do anything he doesn't wish to, especially tests and the like.

[Granted a moody seventeen year old is probably different than a small child]

So I would say that even if she is grudging about her tests, that's better than nothing.