Each test carries its own experimental hypothesis, a prediction for how that test will turn out. Blood samples might reveal higher levels of lactose among anxiety patients. Every one of these hypotheses is testable and therefore scientific whether they're right or not. If the psychic makes a prediction that turns out to be right, you might think that shows the persons really is psychic. You've left no way to show that it's false to believe in that person's psychic ability.
Professional psychics are no more accurate than anyone else at predicting anything .
If you open his head up surgically and see no Martians, he says they disappear when exposed to oxygen. No matter what test you come up with, you never show any evidence of the Martians in his head, but that makes no difference. He always has an explanation. His idea about the Martians cannot be falsified and therefore is not scientific. Your Uncle Zed thinks the sun will not rise in the sky unless it hears a rooster crow at dawn.