This sounds a bit like a 'no true Scotsman' (i.e. the bar would be moved with any example of a bad unit test that needs types), but I would need think more on i

This sounds a bit like a 'no true Scotsman' (i.e. the bar would be moved with any example of a bad unit test that needs types), but I would need think more on it. In my opinion, unit tests need to cover multiple levels, at least two, the units, and also the business logic, and proper types would cover the gaps in between. If anything I would invert the title of this, and say a strong enough type system makes unit tests unnecessary, but I don't think that's anything new and you can see it at work in pure FP languages like Haskell.