Selective Test Execution at Stripe: Fast CI for a 50M-line Ruby monorepo

This post details the technical implementation and impact of Stripe's Selective Test Execution system on a 50M-line Ruby monorepo. It explains how the system analyzes code changes to determine which tests are relevant, allowing Stripe to run only about 5% of its tests on average. This significantly reduces CI times, enabling faster development cycles and improving developer productivity. The post highlights the trade-offs involved in achieving this level of test selection and the engineering effort required to maintain such a system at scale.