As the size of program grows it becomes more difficult to understand the code. Therefore, it is also more likely to accidentally embed bugs when changing code. Ideally, it is desirable to test all existing functions each time we change source code, but it is not easy to test all existing functions frequently as testing takes time and cost. Therefore, it is necessary to consider automated testing. There are many advantages to test automation. Most are related to the repeatability of the tests and the speed at which the tests can be executed. There are a number of commercial and open source tools available for assisting with the development of test automation. One of test automation tools is Selenium. It is widely used around the world as a tool for automating test for web application. In this book we use Selenium WebDriver to perform automatic operation of the browser.