Tests can be great, though it is also easy to write tests that aren't terribly useful. Eg, testing things unlikely to change or are generally unimportant. This can lead to a large amount of test code that needs to be maintained. I think it is easy enough to test the majority of the functionality by just running an animation that exercises all the features (events, bounding boxes, etc). I prefer this over having lots of test code, as I already have to maintain 18 runtimes and Spine itself!
CodeBetter looks interesting. Setting up and maintaining CI can be quite a bit of effort though, especially for so many projects!
Ah, I didn't know about the /// comments so I used the javadoc style. Is it enough to change the /.../ style to /// without adding XML to clutter things? 🙂 It's a bit silly to add <summary> tags around the text for every method, especially when already using a special comment style that indicates the text is documentation. The XML is less bad for parameters, but still quite verbose.