According to research available on the Institute of Advanced Dance Medicine and Science, the topple test (turns from 5th) is used to assess pointe readiness in young dancers. The test essentially demonstrates a dancers ability to use proprioception (sense of balance), and control landing (use of correct muscles). If a dancer is unable to execute a 5th position pirouette without toppling then they are not ready to start Pointe.
The following is a video available on Ballet In Form, an excellent source of technique specific resources. Miss Magali Messac, former Principal Dancer of American Ballet Theatre, and Master teacher of Gyrotonics; discusses and demonstrates the proper way to perform consecutive turns from 5th.
Follow this link to view the exercise.Ba