Programming language tools help get rid of classes of bugs. GC languages help get rid of or reduce significantly classic security bugs such as buffer overflows

Programming language tools help get rid of classes of bugs. GC languages help get rid of or reduce significantly classic security bugs such as buffer overflows, use after free and so on. Static types get rid of other kinds of bugs and unit tests you don't have to write as a result. It, of course, does not solve everything or remove the need for tests. Rust's borrowing system help get rid of multithreaded data race bugs, something traditionally hard to write any sort of fast unit tests for. Other static analysis tools also help you not write tests by testing certain things on everything. Even linting is another kind of automated meta-testing tool. Also for your json 'string typing' example, that is a hint maybe you should use statically defined models instead of relying on unit tests to catch typo bugs?