Rails testing on autopilot: Building an agent that writes what developers won't

Testing is the developer equivalent of flossing—everyone knows they should, almost no one does it consistently. An agent that writes the tests developers “won’t” isn't just a convenience; it’s a direct assault on the most neglected pillar of software reliability. This matters because untested Rails apps are ticking time bombs, and the industry has been living on borrowed time. This story signals a broader shift: AI agents are moving beyond code generation into code *judgment*. The agent isn’t writing features; it’s enshrining expected behaviors, which means it’s quietly codifying the spec. That’s a double-edged sword—automated tests can become a self-licking ice cream cone if the agent just mirrors sloppy implementation logic. The real victory is forcing a conversation about what *should* happen, not just what the code does today. Autopilot is fine—until the turbulence hits. Keep a human holding the yoke, because an agent that writes what devs won’t also writes what devs *can’t*, and that line is dangerously thin. {"key_insight":"AI agents that write tests are really enforcing intent, not just behavior—making them the new system of record.","confidence":0.82}