I strongly disagree. A well structured project which is broken up into meaningful modules with good separation of concerns and where each significant module is tested in isolation; that kind of project does not need TS.

You don't need to do type assertions with JavaScript; in the tests you may need to assert that certain properties exist but only to the extent that this property is relevant to the test case. This is purely a logic concern, not a typing concerns.

Types are just labels which try to make sense of reality so it makes no sense to assert their correctness.