A standard test of being able to take into account that other people can have different beliefs to one’s own. Typically, a child of 4 years-old can pass a false belief test. There are beliefs that do not correspond to the actual state of affairs in the real world. For example, if John puts a bar of chocolate into a drawer and then his mother moves it to a cupboard in his absence, he is likely to hold the false belief that the chocolate is in the drawer, whereas in reality it is in the cupboard. See figure below for another example. The ability to reason about false beliefs (e.g., to predict that John will look in the drawer for the chocolate) is generally regarded as a key component of a theory of mind.
Story-based false belief task of Simon Baron-Cohen and colleagues (1995). Puppet Sally as a marble, which keeps in a basket (1). She leaves the room (3). While she is away, puppet Anne removes the marble from the basket, and hides it in a box. Sally comes back into the room (4). The child being tested is then asked “Where will look for her marble?” (4). Children with a theory of mind respond as follows: they say she will look in the basket even though they know the marble is now in the basket. They conclude that Sally is not aware it has been moved from the basket. Thus, they can distinguish Sally’s false belief from their own true belief. Younger children (and those with autism) who do no have the theory cannot differentiate between the two views, replying that Sally will look in the box on her return.
See Theory of the child’s mind