The testing of applications with a Graphical User Interface (GUI) is a complex activity because of the infinity of possible event sequences. In the field of GUI Testing, model-based approaches based on reverse engineering of GUI application have been proposed to generate test cases. Unfortunately, evidences show that these techniques do not support some of the features of modern GUI applications. These features include dynamic widgets instantiation or advanced interaction techniques (e.g. multi-touch). In this paper, we propose to build models of the applications from requirements, as it is standard practice in Model-Based Testing. To do so, we identified ICO (Interactive Cooperative Object) as one of the modelling techniques allowing the description of complex GUI behavior. We demonstrate that this notation is suitable for generating test cases targeting complex GUI applications in a process derived from the standard Model-Based Testing process.