1 

     2 

     3 assert(List(0,1,4).contains(CW6a.collatz(1)))

     4 assert(CW6a.collatz(6) == 9)

     5 assert(CW6a.collatz(9) == 20)

     6 assert(CW6a.collatz(9000) == 48)

     7 

     8