Model Customization and Agents
Rails testing on autopilot: Building an agent that writes what developers won't | Mistral AI

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

3/11/2026

What this post added

This post details the technical implementation of an autonomous agent for generating and improving RSpec tests in Rails applications. It describes the agent's architecture, which leverages Mistral's Vibe platform, including the use of `AGENTS.md` for step-by-step execution plans and specialized `SKILLS` files for different Rails file types (models, controllers, etc.). The post also elaborates on the integration of custom tools like RuboCop for linting and SimpleCov for test validation and code coverage, including stripped-down code examples for tool implementation. It further discusses metrics for measuring test quality, including tool-based metrics and the concept of 'LLM-as-a-judge' for qualitative assessment.

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