1 

     2 

     3 assert(CW6b.get_delta(None, None) == None)

     4 assert(CW6b.get_delta(Some(50.0), None) == None)

     5 assert(CW6b.get_delta(None, Some(100.0)) == None)

     6 assert(CW6b.get_delta(Some(50.0), Some(100.0)) == Some(1.0))