A "fake" isn't a test; it's a real, working implementation of some interface. The only reason we don't use such implementations in production is for some non-fu

A "fake" isn't a test; it's a real, working implementation of some interface. The only reason we don't use such implementations in production is for some non-functional reason (efficiency, resilience, etc.). For example, if we want a key/value store we might choose Redis for production, but a HashMap is a perfectly good fake (and you can bet that the language/library implementing HashMap has a ton of tests!)