Main character is a boy.
The boy is forced to leave his home for some reason and goes to the forest. There is a druid/wizard character there that might take him on as an apprentice. There are a few others there doing the same thing. They are all give challenges (none of which I remember) in order to weed out those not suited/worthy. At one point the boy might get stuck in a grave. Anyway, the end of the story is the boy figuring out the last challenge. It’s a riddle carved on a tree. There’s a picture in the novel and it looks like Celtic tree script. The solution is to read it upside down. He wins and gets to study magic.
There’s only one book, it’s not a series as far as I know.
The book is probably from no earlier than the early 2000s
The cover I think had a silhouette running across it