Mobile apps testing can be done using Appium, a cross-platform solution for automating native and hybrid mobile apps. Appium acts as an HTTP server that creates WebDriver sessions to run tests on real devices and simulators for both iOS and Android platforms. It proxies commands to the appropriate automation frameworks like UIAutomation for iOS and UiAutomator for Android. This allows writing tests once that can run on multiple mobile platforms using the same WebDriver API and commands.