A development team struggling with low unit test coverage turned to AI tools and saw coverage jump from 28% to 82% in two months. However, three weeks after deployment, a bug in an edge-case branch slipped through—despite that code having 100% test coverage. This incident exposes a fundamental limitation of AI-generated tests: they excel at covering common paths but often fail to capture nuanced business logic and boundary conditions. The team learned that high coverage numbers can create a false sense of security. For engineering leaders, this underscores the need to complement AI-generated tests with human-designed edge-case scenarios and property-based testing. The signal is especially relevant as more teams adopt AI-assisted development workflows.
A team's AI-generated tests achieved 82% coverage but missed a critical edge-case bug, revealing the limits of AI in testing.