Appium is an open source automation testing framework for use with native and hybrid mobile apps. It aims to be language and framework agnostic, meaning it can work with any language and testing framework of your choice. Appium can test iOS, Android and Windows applications, even if they are hybrid. It uses the WebDriver protocol to automate any mobile app from any language and any test framework, providing full access to backend APIs and DBs from test code. The article demonstrates how to use Appium for testing a React Native hybrid app using Python's py.test framework. It covers topics such as setting up Appium, connecting to it from a test case, identifying elements on the screen, waiting for transitions between pages, and writing tests for different scenarios like login errors and successful logins. The article provides examples of how to write tests in both iOS and Android React Native apps.