I mean, look at the number of tests needed to replace a few lines of types. You have to check the behavior of your functions for all kinds of invalid inputs. With typescript you still need tests but less of them. And also you can get rid of a lot of input validation in your production code.

It’s not either/or. Nice strawman you put up here.

No I didn’t. The statement was that Typescript solves the listed issues, which is obviously not true. There may be of course discussion whether TS _helps_ to solve such issues but you won’t be able to convince me that TS _solves_ e.g. lack of testing.