Most schools use the NBME Shelf exams. We had those exams for all the rotations, plus orals and other various exams depending on the specialty (Psych had a big 25 page paper, IM had EKG and Chest radiographs). So yes you do but usually only one every month to two months and I had very very few during the fourth year. Only in Ophthalmology, ICU and radiology did I have an exam.
After every rotation, including some electives, there is a "shelf". Paper test, 100 multiple choice questions in 2 hour time period. The questions are pretty long sometimes. PreTest books are quite helpful. Good luck in the coming years!