Final answer:
The assumption made by a therapist using the Rep Test is that the client's cognitions are not related to their behavior.
Step-by-step explanation:
The Rep Test is a projective test that is used by therapists to gain insight into a client's unconscious desires, fears, and struggles. One assumption that is made by a therapist using the Rep Test is that the client's cognitions are not related to their behavior. This means that the therapist believes that the client's thoughts and beliefs may influence their behavior, but they are not the sole determinant of their actions.