You can't just go take it anymore.
"Pilots applying for an ATP certificate with a multi-engine class rating or jointly with a type rating after July 31, 2014 must satisfactorily complete an airline transport pilot certification training program (ATP-CTP) before applying for the ATP knowledge test. The ATP-CTP course is an informative program including 30 hours of ground instruction covering a myriad of subject matters including aerodynamics, weather, air carrier operations, and 10 hours of simulator time. For many pilots, this is their first introduction to real airline training and training in the airline-oriented full-motion simulators. Following the ATP-CTP course, candidates must pass the ATP knowledge test."