A test suite going green tells you one thing: the assertions you wrote passed. It does not tell you that the property you actually care about holds. Those two things usually overlap. On a recent piece of infrastructure work — a system meant to coordinate independent actors under a set of hard invari...

We had a shared secret scanner. We had a comment saying it covered every path that assembled context and sent it to an external model. Both were true right up until they weren't: one assembly path had quietly grown up without ever inheriting the scanner. Nothing detected the gap, because the claim o...