code: def _expected_argument_string(self):
          
  
          if self.args is _any and self.kwargs is _any:
              return 'any args'
          elif self._custom_matcher:
              return "custom matcher: '{}'".format(self._custom_matcher.__name__)
          else:
              return build_argument_repr_string(self.args, self.kwargs)
docs: Generates a string describing what arguments the double expected.
  
          :return: A string describing expected arguments.
          :rtype: str