How I Used AI Agents to Migrate Reka UI's Tests to Vitest Browser Mode

I wanted to learn Vitest Browser Mode properly. Not with a counter component. Not with five tests written specifically for a demo. I wanted a real component library with years of testing history and enough sharp edges to punish bad assumptions. So I created a working fork of Reka UI and used AI coding agents to migrate its test strategy away from jsdom. The original suite had 97 test files. Eighty-seven touched the DOM and received Browser Mode counterparts. The remaining ten contained 571 DOM-free tests, so they moved to a plain Node project instead. I kept every original jsdom file as a comparison corpus. This gave the agents a live baseline rather than a memory of what the old tests used to do. The AI didn’t only translate tests. It reviewed ports, introduced deliberate bugs, ran both environments, recorded findings, and improved its own prompts after each batch. That process is the interesting part. This work lives in my [Reka UI Browser Mode…