> My favorite definition of “legacy code” is “code that is not tested” because no matter who writes code, it turns into a minefield quickly if it doesn’t have tests.

Unfortunately, "tests" don't do it, they have to be "good tests". I know, because I work on a codebase that has a lot of tests and some modules have good tests and some might as well not have tests because the tests just tell you that you changed something.