Perfectionistic Son

My son has always been somewhat of a perfectionist. He always wants to play his best at sports and cries when he has a bad game. He has always had good grades and I have always told him that if he tries his best, that is the most important thing. The problem is that every time there is a big test in school (he is in the 7th grade), he studies, asks me to quiz him and if he gets an answer wrong he starts crying, he wakes up the next morning and goes straight for the text book and begins to cry as he studies again. He asks me to quiz him and again, if he misses something, he is in tears and says he doesn't know it and he is scared he's going to fail. He has always gotten mostly A's and some B's. I try to tell him that I understand that this test is important to him and I understand his fear that if he doesn't know it he could fail a test. I also try to ask him the question What's the worst that could happen? That he fails the test. Did he try his best? Did he feel satisfied with the amount of studying he did? Can he see himself with an F and still work hard in class and do better on the next test? I don't know what else to do? I explain to him that if he continues worrying so much that it puts him in tears every time he studies for test, gets quizzed for the test, he will make himself physically ill. I have had an ulcer and he knows what that was like and how painful. I tried to explain how important it is for him to stop, take a break, take a deep breath, go to sleep on time, study in the morning when he's had time away from the book. I need to know what else I can do because I don't want to increase his stress level, his fear and I can't handle seeing him cry every time there is a test. Help