Some animal tests on primates are okay, as long as they don't cause injuries, illnesses, or other harmful lasting side effects on the animals. Some neuroscience testing may be dangerous to both humans and primates, so other options like some kinds of computer simulation should be investigated as possible alternatives.
Animals are not sentient creatures. They don't exist at the same level that humans do. Humans are a simply a higher form of existence. As long as the experiment can be clearly shown to benefit humanity, I see no reason why we shouldn't conduct these tests. If we were to stop using animals to conduct experiments, drug testing and other research would slow to a snail pace.
Animals subjected to testing have no quality of life in labs, and scientists give them no choices. There is no way to measure the suffering they endure, including lack of comfort and affection during the time they find themselves subjected to painful procedures they cannot understand. It is wrong to cause that kind of suffering when there appears to be so little proof available to the public that the tests make any great impact on human medicine.
No, it is not ethical to test on animals because animal rights exist and all creatures should be treated fairly. Who are we to say which animals can be tested on and which cannot? Where do we draw the line? Animals should live freely and not be subjected to human testing.