The paper deals with test automation of GUI (General User Interface) softwareusing simulations. The development of GUI software requires a greatamount of time and cost concerning the testing aspects. In order to facilitateand speed up the testing of such GUI software an approach basedon discrete-event modeling and simulation is proposed. Traditionally, theGUI software test automation approaches require the development of testingprocedures which are fastidious to carry on. The idea is to perform testautomation of GUI software by integrating of existing GUI software testingenvironments within a DEVS (Discrete EVent system Specification) formalismframework called DEVSimPy. The proposed approach is validatedon a real application dealing with medical software which have to respectvery strict formats defined by French governmental institutions.