When implementing the window driver pattern, you should write the equivalent of a device driver for each part of your GUI. Acceptance test code only interacts with the GUI through an appropriate window driver. The window driver provides a layer of abstraction, which forms part of your application driver layer, to insulate your test code from changes in the specifics of the UI. When the UI changes, you change the code in the window driver, and all of the tests that depend upon it are fixed. The window driver pattern is shown in Figure 8.3
