Hmm... I agree on type level correctness with you.
But, this goes onto the critical issue with TDD, most people misunderstand it and tend to talk about the code coverage metrics where it all got wrong.
Suppose you do TDD on the business rules metrics and 99% of them are well tested, meaning all the behavior your code is correct (from the business perspective)... would you really care about type level correctness?
As for the NoRedInk example, this got to do also with the TDD and it's an exceptional case IMO.
People tend to test JS frontend code, and what is JS mostly doing? it manipulates the DOM / BOM... UI stuff.
Basically UI testing is glue testing, you change the UI tomorrow, and you gotta change the tests too. It's like testing 1 + 1 = 2.
That's where elm typing is really great, you don't need to test UI, however you verify what you're doing with typing ;)
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