dommy

https://github.com/takahashim/dommy

A pure-Ruby DOM polyfill on top of Nokogiri::HTML5, a Ruby-side analogue to JavaScript DOM libraries like happy-dom and jsdom. It exposes browser-like DOM semantics — events, MutationObserver, Custom Elements, Shadow DOM, the File API (Blob / File / FormData / DataTransfer), URL, Promise, timers, and Storage — without spinning up a real browser. Aimed at testing Ruby code that emits or consumes HTML. Includes drop-in RSpec matchers and Minitest assertions.