[bobziroll]

I imagine it would be very difficult to teach a topic no one is familiar with by teaching how to test it _first_. A TDD approach to teaching a brand new topic would be very hard to follow and require the viewer to go back to re-watch the testing portion. (Imagine teaching a total beginner how to test a function before teaching them what a function even is...)

However, I think there's a lot of validity to the idea that every tutorial should include lessons on how to test it that new topic, and even give examples of how to implement a TDD approach. But those lessons would (IMO) have to come after the initial parts of the tutorial that taught the concept first.