proxyquire-universal is a Browserify plugin that enables developers to write tests using proxyquire for Node.js and automatically switch to proxyquireify for browser environments without modifying test code. It's designed for developers building JavaScript applications with Node.js and Browserify who want consistent mocking behavior across both environments. The tool handles the plugin registration automatically, making it a seamless drop-in replacement for proxyquire when bundling tests for the browser.