The most important thing here seems to be "For every part of my code change, if I break the code, will a test fail?". Or as I'd put it "if you break the code de

The most important thing here seems to be "For every part of my code change, if I break the code, will a test fail?". Or as I'd put it "if you break the code deliberately does the test actually fail?". Seen quite a few tests in my time that don't capture the functionality they think they are. They pass but wouldn't be able to tell if the underlying functionality they capture is genuinely broken. This is why I guess the standard practice is to go test red before you go test green.