[EdSharkey]

I like your "toolkit" metaphor for test-ability in any case.

If you had asked me a year ago if you could Test-Drive UX development, I would have said no, UX tests are too brittle, and that one should just visually inspect them and focus on testing the data flowing to the view and commands flowing from the view.

But then I got some exposure to the Jest framework for testing and was blown away in that they've automated the acceptance testing and automated accepting changes to expected outputs in order to mitigate the brittleness problem.

And before that I learned about the Quixote framework for CSS testing and learned I could TDD my CSS code (to some extent), making that development more deterministic.

These tools completely transformed my beliefs about what the UX development process could be.