Code review comment for lp://staging/~submarine/unity-scope-evolution/evolution-previews

To speed things up a bit, I've pushed a fix for my AttributeError gripes to this MP.

I also noticed that results were being added twice, so I fixed that while I was fixing how the tests injected the data.

The branch could probably do with a test for the previews, but I've had trouble hooking that up right for previews that depend on result.metadata, so I won't complain on that count.

I'm changing my vote to "approve", but I'd appreciate if someone looked over the changes I made.