Pesticides are tested on animals. How relevant is that for humans?

Although animals are not "little people in fur," and results from animal tests have to be interpreted carefully, they can be very relevant for humans.  Pesticides usually cause toxicity to cells or molecules, and the cells and molecules of humans and animals can be very similar. Thus, if a pesticide affects a cellular or biochemical process in animals, it is likely to do so in humans as well.

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