Most JavaScript test runners default to synthetic DOM environments like jsdom or happy-dom, which fall apart at the boundaries where tests need to verify real browser behavior. This guide walks through setting up Vitest's browser mode for component testing, writing tests that leverage real browser APIs, and migrating from Playwright Component Testing. Note on versions: This article describes Vitest's browser mode using APIs such as @vitest/browser/react , expect.element() , and built-in browser orchestration. Before following these instructions, confirm your installed Vitest version supports these features by checking the Vitest release notes and your installed package's documentation. All examples assume you have verified API availability against your specific version.…