i think it all depends on how your grades are from undergrad. some people i know that were placed in the a semester other than 1st in premed were persons who got a B or above in the class and therefore they did not need to take it over, i think it also depends on your overall performance at your previous school.
i have some friends that took premed 3 and they were already certified nurses and paramedics. the dean of premed also looks at your grades and decides on a "modified" premed programme for you which excludes the classes that you would be given credit for.
as for a placement test, there was one for me when i entered premed. they tested us on pre-calc, chem, and english.
this is really just what i know from my experience, can't speak from an official point of view. hope this helps

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