Originally published on sergei-parfenov.com . A bug fix can make every new test pass and still introduce a regression. Here is a deliberately constructed Python example, checked locally without an LLM. An order filter has three requirements: Omit the filter, or pass None : return all orders. Pass an empty list: return no orders. Pass a list of statuses: return only matching orders. The reported bug is that omitting the filter returns nothing. This proposed fix looks reason...