docs: def returns(self, val):
          """Set the last call to return a value.
  
          Set a static value to return when a method is called.  I.E.::
  
              >>> f = Fake().provides('get_number').returns(64)
              >>> f.get_number()
              64
  
          """
          exp = self._get_current_call()
          exp.return_val = val
          return self