Defect leakage

Defect leakage happens when bugs slip through testing and show up later—whether during UAT, in production, or in later development phases. It signals that your testing process has gaps or blind spots that need attention. Think of it like holes in a security net that let issues pass through undetected.

Consider a mobile banking app that undergoes thorough testing before release. The team tests transaction flows, validates security measures, and checks performance. After deployment, users discover that recurring payments fail when scheduled across daylight savings time changes. 

This time-zone related bug wasn't caught because test scenarios didn't account for this specific calendar condition. It leaked through despite extensive testing, costing more to fix in production and temporarily disrupting users' automatic payments. 

Defect leakage costs significantly more to fix than catching bugs early. When defects reach production, they can damage user trust and your company's reputation. High leakage rates also indicate problems with your testing process—maybe you're missing key test scenarios, using unrealistic test data, or not testing in production-like conditions. 

Finding the root cause of leakage requires deep analysis. Did tests miss the scenario? Was the test environment too different from production? Were requirements unclear? 

Teams often struggle to reproduce leaked defects because production conditions can be hard to replicate in test environments. Successfully reducing leakage means improving multiple aspects of testing—coverage, environment fidelity, requirements clarity, and test data quality.