Ruby on Rails

Mistral Builds Autonomous Rails Test-Writing Agent Using Vibe Coding Assistant

Mistral's Applied AI Proto team built an autonomous agent that reads Ruby on Rails source files and generates or improves RSpec tests with no human intervention, running in parallel across large codebases inside CI/CD pipelines. The agent is built on Vibe, Mistral's open-source coding assistant, and uses context engineering via AGENTS.md files, per-file-type skill files, and custom tools for linting and coverage validation. Key techniques include forced self-review prompts, specialized skill files per Rails file category, and careful handling of shared RSpec factories. The approach improved a quality score from 0.68 to 0.74 through structured prompt engineering alone.