How to log on test end

[Boltzmachine]

I want to call the metric.compute only once since computation takes a lot of time. And I know self.log will call metric.update. Therefore, I only want to compute it at the end of test. So I log the metric in on_test_end.
However, I got

You can't `self.log()` inside `on_test_end`. HINT: You can still log directly to the logger by using `self.logger.experiment`

So how to log the metric at the end of test. (I saw the hint but I am not sure if it has the same effect as self.log)