Some follow up from creating a new project and adding tests.
This turned out to be important...
I hadn't really noticed in the last one but I hadn't added the new classes to the test target, as I would under Obj-C. In Swift 2 there's a new @testable keyword. I found it blogged by Natasha the Robot when I started looking to find out why I wasn't seeing any code coverage showing up for my classes.
Then I started wondering why I was getting Undefined Symbol errors. I could resolve them by including the classes, but then I wouldn't get coverage and everything I saw on @testable assured me I didn't need to include them. Finally, I remembered I'd been getting a bit click happy earlier. I'd disabled Allow testing Host Application APIs.
One checkbox later and I'm a happy camper...
Okay, not a lot done tonight but I feel like a few pieces fell into place.