“Antidotes!” said Snape, looking around at them all, his cold black eyes glittering unpleasantly. “You should all have prepared your recipes now. I want you to brew them carefully, and then, we will be selecting someone on whom to test one. . . .”
This is a sentence from Harry Potter and the Goblet of Fire.
What's the meaning of
on whom in this context? Could I just omit it?
Thanks in advance.