Why Devin, Cursor, Factory, and other coding agents cant test the code?

A new study found that stopping AI coding agents from writing their own tests made them a bit more successful. They were also 6% faster and 9% cheaper. That sounds backwards until you see why. The agent’s tests just repeated its own reading of the requirement, so they passed by default. You pay more and get no real check. The lesson isn’t “skip testing.” It’s “don’t let the builder be the only checker. That’s the gap Kane CLI fills. It sits in the terminal next to Claude Code, Cursor or Codex. It takes a plain-English user flow, runs it end to end in a real browser or on a real device, and sends failures back to the coding agent. Coding agents write the code. Kane CLI checks what users see. Try Kane CLI Now: https://www.testmuai.com/kane-cli/