As mentioned previously, there are several frameworks and tools available to test PHP and Magento code:
Ecomdev_PHPUnit: This extension is just amazing. The developers at Ecomdev created an extension that integrates PHPUnit with Magento and also adds Magento-specific assertions to PHPUnit without having to modify core files or affect the database.Magento_Mink: Mink is a PHP library for the Behat framework that allows you to write functional and acceptance tests; Mink also allows you to write tests that simulate user behavior and browser interaction.Magento_TAF: This stands for Magento Test Automation Framework and is the official testing tool provided by Magento. It includes over 1,000 functional tests and is very powerful. Unfortunately, it has a major drawback; it has a large overhead and a steep learning curve.