That's not really fair, they ported their stack so front end and backend share type definitions. It was not a fashion driven decision. Wrt to types and tests,

That's not really fair, they ported their stack so front end and backend share type definitions. It was not a fashion driven decision. Wrt to types and tests, "Types" means some verifiable annotations on the code. If a type system can encode enough information in them, perhaps with preconditions or other contracts, then would tests be superfluous? If so, I don't get your assertion about tests and dynamically typed languages. On the other hand, since typescript is unsound, shouldn't you really test like a dynamically typed language?