Functional tests mimic the user interaction with our application. They literally mean testing in the form of browser interaction, which involves clicking on the page, adding products to the cart, and so on. For this purpose, Magento uses Magento Testing Framework (MTF). It's a PHP wrapper around Selenium, which is a portable software testing framework for web applications. MTF is not available out of the box via the console. It can be downloaded at https://github.com/magento/mtf.
The following requirements need to be met before installing MTF: