Four Ways a Test Can Lie to You
ken_walger·
Ken Walger unpacks the subtle ways software tests can deceive developers, focusing on green or red test results that fail to validate actual system behavior. The post illustrates how claims proposed by AI coding agents or developers require human verification, yet can quietly lose validity or recency without triggering failures. Through concrete examples—such as overlapping logic where two separate mechanisms exclude an edge case—he demonstrates how clause deletion goes unnoticed because no assertions turn red. To prevent silent test decay, Walger advocates for pairing assertions: whenever a test claims that a feature or flag has no side effect when disabled, it must be matched with an explicit assertion proving the expected effect occurs when enabled. For developers aiming for staff-level architectural ownership, mastering test fidelity is essential; brittle or misleading test suites undermine confidence during domain refactoring and system evolution.