Green Tests Can Hide Bugs: Why Passing Assertions Don't Always Mean Correct Code

A developer discovered that a PostgreSQL integration test was passing for the wrong reason during routine testing. The test was designed to verify that querying a non-existent Company record returned a 'not found' result, but an invalid non-UUID value was used as the lookup ID instead. PostgreSQL rejected the malformed ID before Prisma could check for the record's existence, causing the repository to return a failure rather than the expected missing-record outcome. Because the test's assertion was placed inside a conditional success branch, the failure path bypassed it entirely, allowing the test to complete without any failing assertion. The fix involved using a valid but never-inserted UUID and asserting the full result object directly, ensuring the test genuinely exercises the intended code path.