We had something similar, only it was more than just tests. When a course ended, many people made "bibles", which typically contained their lecture notes, any handouts, problem sets and answer keys, midterm and final exams and answer keys, and anything else relevant to the course (formula sheets, etc). Most GLOs, some dorms, and a few other student organizations had libraries of these bibles - if you knew you'd never use the material again, you could donate your bible to the library, and if not, you could still loan it out privately. Most profs changed things up enough every year that you couldn't get by with copying and pasting; I never met a prof who forbade the use of bibles, and some actively encouraged it.
One of my sisters, who shared my major, was a year ahead of me, and had top grades, loaned me a few of her bibles. They helped immensely. Even if it was a different professor teaching the course, sometimes one prof would go more into depth on a particular topic, while another would gloss right over it (then nail you with it on the final
). And the old problem sets and exams usually made great practice questions.