But "untested" is not the same as "unverified". There are other ways to verify code. E.g., I design my code algorithms as English language or math-based specs, and mentally verify them, before translating them to code. Using that method, I have never - not even once - discovered in code created that way. Yet such code has no unit tests. Instead, I write behavioral tests, and the only time they fail is when there is an error in the test itself.