WebDriver Action Builder class can be used to take control of the mouse cursor on a web page when writing web browser automated tests. This can be very helpful for writing tests where elements on a web page only appear on actions such as mouse move or hover over.
WebDriver Action Builder Video Tutorial
Sometimes elements remain hidden in the html source code until the mouse cursor is positioned over an element. For such scenarios the Action Builder class is an ideal technique to use as it allows the programmer to simulate such scenarios.