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

Mistral AI built an autonomous agent that reads Rails source files, generates or improves RSpec tests, and runs unattended in CI/CD pipelines. The agent is based on Mistral's open-source coding assistant Vibe, using a repo-level AGENTS.md, skill files divided by file type, and custom tools for RuboCop and SimpleCov.