> Then you need to make those functions public, […] That depends on the language, but often there will be a way to expose them to unit tests while keeping them

> Then you need to make those functions public, […] That depends on the language, but often there will be a way to expose them to unit tests while keeping them limited in exposure. Java has package private for this, with Rust the unit test sits in the same file and can access private function just fine. Other languages have comparable idioms.