Plus Rust by design avoids all sorts of bugs leading to less tests imo. Python for example you really want a lot of testing, maybe even contracts, but with Rust I find that many of those tests are irrelevant.
This assertion on the amount to tests makes no sense at all. Tests are not about language features. Tests are about checking invariantes, checking input and output bounds, and checking behavior. Tests focus on the interface, not the implementation. Tests only work if test coverage is high.