@typhonjs-utils/build-test-browser is a development tool for building and testing TyphonJS packages across Node.js and browser environments. It streamlines dual-browser/Node ESM package development by providing test runner code, coverage reporting with nyc and rollup-plugin-istanbul, and a minimal static web server using polka and sirv. This tool is designed for developers creating TyphonJS modules who need to run the same test suite in both Node and browser contexts with features like Mocha integration and headless Chrome testing via puppeteer-core.