I've been working through the exercises in the excellent iOS Unit Testing by Example book by Jon Reid, which I highly recommend. However, the book is in beta at the moment and there are some curveballs thrown by iOS 13 that aren't handled in the text yet. Specifically, when I hit the section about using a testing AppDelegate class I thought "This is very good. But what about the SceneDelegate?"

That kicked off quite the odyssey to be honest. If this is interesting to you I wrote up a Gist documenting what I found, and a partial solution to the issue.