Exactly. Code can pass 100% of tests--but the tests only cover what the test writer knows about. Code, especially old code, can encapsulate TONS of weird human and business specific behavior that you don't know about or doesn't seem sensible at a quick glance. Don't be so quick to dismiss old code--people rarely set out to build something thats shitty and code, especially code that seems completely asinine, is rarely just in there for the lulz.