Coverage, Quality, and Goodhart's Law

Explore how to effectively use code coverage as a programming tool rather than falling victim to Goodhart's Law in this 58-minute conference talk from NDC TechTown 2025. Learn why coverage metrics often fail when used as targets and discover three common but problematic approaches: not measuring coverage at all, measuring but ignoring it, or setting arbitrary thresholds that break CI pipelines. Understand how coverage serves as a crucial component in safety-critical systems like automobiles, aircraft, and spacecraft, and discover how to leverage it properly for software quality improvement. Dive into practical demonstrations using GCC 15's coverage capabilities to identify gaps in test suites, experiment with program representation and visualization techniques, and transform coverage from a misused metric into a valuable development tool that guides testing and correlates with quality.