The tests exist as a way of determining if someone did the action of copying which is the important thing at the core of it. And in this case the facts aren’t really in dispute, it’s whether what GH is doing counts as copying.

If you had a really really good memory and remembered almost exactly how your former company implemented something and when faced with a similar problem unknowingly produced similar code. It’s iffy as to whether this is copying. Because it really probably isn’t — you’re allowed to learn from copyrighted works — but the courts aren’t omniscient and when presented with the code they very well may rule that copying was more likely than not.

But we are omniscient in this case so we don’t really need the tests. Is what GH does more like copying or learning? This isn’t something that can be determined purely from the output of the tool.