Animal testing is a great benefit to people, in my opinion. The major pro of this testing is that it allows people to test drugs and other such things to be sure (or as sure as possible) that the drugs will not harm people. If there were no animal testing, we would have to take new drugs or new chemicals and test them on people. We would essentially have to just guess that something wouldn't hurt people.
The only real con is if you are an animal. It is surely horrible to do these things to animals -- give them cancer, things like that. But this does not, in my opinion, harm human beings in any direct way.