Developer warns against merging code suggestions without testing on clean environment

A developer described an incident where a suggested code fix passed local tests but would have failed on a clean system. Their local machine contained cached packages and environment variables that a fresh runner would lack, masking the actual bug. The issue involved a checkout helper returning an incorrect currency code when a required locale package was missing, which their laptop already had installed. They emphasized the need to test patches on a completely clean environment before merging to avoid false positives. The developer now follows a strict process of capturing failure logs and testing on isolated hosts to ensure reproducibility.