A "mock-up" is something that is not the real thing, but almost; a model for the real thing. For example, magazine compaies do mock-ups for each page, then layout the real page that goes to the printer.
A "mock" election would be just like the real thing, a model, or imitation.
I think that your teacher means "practice baccalaureate, which means to practice the ceremony so everyone knows where to stand and what to do before the real event. :lol: