It's a place to put intetion that isn't so much of a second class citizen that it will likely be ignored and/or not updated if it ceases to be true. You want your test methods fine grained (many methods that each check one variation, instead of one method that checks a whole list of them) and every extra redundancy (method naming vs the variation of data actually passed vs documentation) increases the the chance of those redundancies getting out of sync.

In fact I've occasionally found myself writing reflection code to parse the test method name as input just to avoid that problem altogether (for name and data, not for documentation). And that was in plain Java even, the pattern could be far more useful with that kotlin naming freedom.