Shallow means a person who views potential romantic partners, friends, or acquaintances mainly according to physical appearance, wealth, popularity, and other worldly factors outside of personality. You should always test to see who is shallow and stay away from them, or at least not be loyal to them if you have to interact with them in class, work, or an organization. People like this will betray you the moment you don't have anything left for them to benefit from. They only love, want to befriend, or want to interact with you because you have something they want. They don't necessarily like you as a person. This is my definition of shallow. Stay away from people who are like this!
As a way to test their shallowness, you can lie to them that you're poor, have no friends, don't drive, or put something on your face to make it look like acne zits/scars or moles. Then if they value you less as a human being because of this, give you dirty looks, shy away from interacting with you, or refuse to romantically like you because of these reasons - given you have a lot of attractive strengths to offer - never talk to them again. If you have to, never share anything with or make sacrifices for them. Never be loyal to them. Period. Why would you want to associate with people like that?