If the production code does something by happenstance I will consider it a bug and fix it (unless in Legacy Code, where a bug could mean hidden super-valuable-f

If the production code does something by happenstance I will consider it a bug and fix it (unless in Legacy Code, where a bug could mean hidden super-valuable-for-customers feature). I.e.: I will make sure that this test fail and all other tests pass. Production code doing something, that is not defined by tests is generally not a good idea, because this is clearly an untested functionality. And it has to be eradicated if nobody needs it (business and customers) or it should be covered with a test, and I want to see this test fail (by applying Mutational Testing).