Expecto Patronus Test
A patronus is a positive force that can send messages or protect you. A patronus almost always takes the form of an animal, but can be non corporeal, which means it takes the form of a mist. The incantation needed to make a patronus appear is "Expecto Patronum". While you saw this, you have to think of the most powerful happy memory that you can think of.
A patronus is best at protecting you from Dementors and Lethifolds. Besides that, they are only useful for sending messages. Your patronus takes the shape of an animal that fits your personality.