Oh, where to start. Actually, two-way binding is super easy to test. You provide your object to the View and then perform your operation and then look again at the object you passed in, which you still have, to see how it changed. I cut my TDD teeth on FlexUnit before moving to Karma/Jasmine and AngularJs.
By contrast, the way hooks un-invert inversion of control means that in order to get your data into your View for tests, you either need to have a very deep knowledge of what all those Providers are doing to provide the minimal state needed for your View or you have to essentially bootstrap the entire business-logic state of your app in order to run tests, which is often impractical because it means you need to mock out every endpoint that could potentially be hit. And that means, again, either you have a deep knowledge of that logic or you just blindly hit them and mock them, hit them and mock them, till you have no more errors. All to test a View.
It actually feels like you've never done TDD, you just read somewhere hooks are testable.
But really what I was talking about with footguns is the fact that most devs don't understand the implications of the fact that every render is a new closure. Did you know that when you call useSelector(), often when the underlying value changes the _function returned by that_ is now a new function and needs to be added to the dependencies of any useEffect, useMemo, or useCallback that uses it? The React docs act like the point of using useCallback and useMemo is just to prevent rerenders, but there are all sorts of knockon effects from using it or not using it that are very difficult to reason through. I wrote this recently, and it's only close to accurate because there's no way I could fit all the edge cases in the diagram. https://medium.com/javascript-in-plain-english/should-you-use-usecallback-in-react-e6ad775bd713.
Here's another thing I wrote about how hooks are misleading https://medium.com/codex/everything-you-thought-you-knew-about-react-functional-components-is-wrong-baf2dfc4f6f. Be sure to follow all the links. In short, if you don't see how hooks are a footgun, it's because you have no idea how they work.
