Green Unit Tests Missed 19 Real Bugs Because Reachability Was Never Verified

A software developer building a publish-blocking gate system for a monetization agent discovered 19 blocking defects after asking a verification agent to actively break the system rather than read its passing tests. Every gate in the pipeline had a green unit test, yet three defects were found directly beneath tests that had never failed. The core problem was that unit tests confirm what a function does when called, but do not verify whether production code actually calls it, whether values survive serialization between components, or whether failures are correctly reported. One illustrative gap involved a gate silently removed from the dispatch pipeline — its unit tests kept passing because they never checked whether the gate was wired in at all. The author argues this is a systemic issue beyond any single codebase, requiring independent reachability checks and round-trip persistence testing alongside standard unit tests.