docs: def get_time_spent(self):
          """Gets the total time spent taking this assessment.
  
          return: (osid.calendaring.Duration) - the total time spent
          *compliance: mandatory -- This method must be implemented.*
  
          """
          # Take another look at this. Not sure it's correct:
          if not self.has_started or not self.has_ended():
              raise errors.IllegalState()
          if self._my_map['completionTime'] is not None:
              return self.get_completion_time() - self.get_actual_start_time()
          else:
              raise errors.IllegalState()