docs: def formatted_args(self):
          """Format call arguments as a string.
  
          This is used to make test failure messages more helpful by referring
          to calls using a string that matches how they were, or should have been
          called.
  
          >>> call = Call('arg1', 'arg2', kwarg='kwarg')
          >>> call.formatted_args
          "('arg1', 'arg2', kwarg='kwarg')"
  
          """
          arg_reprs = list(map(repr, self.args))
          kwarg_reprs = ['%s=%s' % (k, repr(v)) for k, v in self.kwargs.items()]
          return '(%s)' % ', '.join(arg_reprs + kwarg_reprs)