[IshKebab]

That's stupid the language you write in has a huge effect on how you test and ensure quality results. They aren't separate things.

E.g. at one end of the spectrum you have Python where you have to write explicit tests for typos and type errors.

At the other end of the spectrum you have formal verification languages like Dafny that may not require any tests to be written.

Rust is somewhere in-between. It has a very strong type system and lots of features that make memory errors and business errors less likely than in most other languages. You still need some tests, but not as many as with C/C++, Python, JavaScript, etc.