Loooong time ago when I did my license (around 2009?) it was possible to use your own car in the test. I did so.
However, then you needed to actually take the test. If you used the provided cars, the teachers would teach you tricks like “ok you drive backwards till you see this tree in this window, then you completely turn the wheel left, then drive slowly until that pylon lines up with that randomly placed piece of black tape in that window…”
Explains the driving skills of some people, right? ^^