So I remember this story from years back, but cannot for the life of me find it.
It started off with a mage having his final exam at the academy where he has to fight his friend, and is supposed to lose, he wins instead and the headmistress punishes him severely sexually.
He is then taken by carriage to the army where he is tested for his magical aptitude, but because of the previous night he tests so poorly he is put into the beginner basic training. During that training he ends up being tested by combat against a plant mage and wins.
That is a fairly fragmented bit of what I remmeber, and I am hoping that someone can nail down what story this is.