Selenium

What is Selenium?
Selenium is a tool that provides a set of libraries and APIs that can be used to automate Web browsers, primarily for testing purposes.

Now Selenium Suite has four components:

1. Selenium IDE: This is a component of Selenium Suite that allows you to automate web browser without writing any scripts or code. You can record your steps on the Web browser and create automated test scripts. We call this record-and-playback.

2. Selenium WebDriver: This is the core of the Selenium suite. It provides a library of classes, interfaces and APIs for controlling web browsers through code or programs.

3. Selenium Grid: Grid is a distributed framework with its own server (hub) and machines (nodes) to run scripts on multiple browsers and machines. We will discuss this in detail while discussing about parallel testing.

4. Selenium RC (deprecated): The predecessor of Selenium Webdriver, it used to provide a server to communicate with Web browser to run scripts.

So, basically the Selenium IDE records and generates scripts that can be run by the Selenium Webdriver.

Selenium Webdriver communicates with Selenium Grid Hub to distribute the test execution to multiple Grid Nodes, each of which might be running a specific Operating System and a specific browser.