def METHOD_NAME(self):
    output = mock.create_autospec(output_lib.Output)
    w = writer_lib.Writer(output)
    w.add_scalar("foo", 42.0, 12, description="fooful")
    output.emit_scalar.assert_called_once()
    _, kwargs = output.emit_scalar.call_args
    self.assertEqual("fooful", kwargs["description"])