Testing a GUI's visual behavior typically requires human testers to interact with the GUI and to observe whether the expected results of interaction are presented. This paper presents a new approach to GUI testing using computer vision for testers to automate their tasks. Testers can write a visual test script that uses images to specify which GUI components to interact with and what visual feedback to be observed. Testers can also generate visual test scripts by demonstration. By recording both input events and screen images, it is possible to extract the images of components interacted with and the visual feedback seen by the demonstrator, and generate a visual test script automatically. We show that a variety of GUI behavior can be tested using this approach. Also, we show how this approach can facilitate good testing practices such as unit testing, regression testing, and test-driven development.