In 2004, a developer at Sun Microsystems was tired of breaking builds. He wrote a small tool as a side project to catch his own mistakes. That tool became Hudson, then Jenkins, and it ended up teaching the entire industry a habit: run the tests on every commit, automatically, forever.

Twenty years later, the same developer, Kohsuke Kawaguchi, co-founded a company whose core product is built on a very different idea. Use machine learning to predict which tests will fail for a given change, and run only those. His early customers reported cutting test execution time by 90 percent. The tool now ships as CloudBees Smart Tests.

The man who made it cheap to run ten thousand tests per commit is now working on running a fraction of them. That is not a contradiction. It is the same problem seen from both ends, and it tells you something honest about where AI actually fits in developer tooling.…