Abstract: A method for testing programs running under a Graphic User Interface (GUI) is provided. The method is especially adapted to work with GUI's operating in a network based display architecture, such as the X11 server release of X Window. The invention provides a mechanism to test several GUI based programs simultaneously while also allowing normal interactive workstation activities to continue. The invention does not require the use of a special X11 server, or the relinking of tested code. The invention may operate using either of two approaches, depending on the capabilities of the window system being used. The first approach uses a mechanism that duplicates the contents of a window into off screen storage. Since this memory copy of a window is guaranteed to be identical to the on screen window, it can be read in place of the screen contents to test for proper drawing.