Web Services fall under the so-called emerging technologies category and are getting more and more used for Internet applications or business transactions. Since web services are used in large and heterogeneous applications, they need to be reliable. So, we propose in this paper, a robustness testing method which generates and executes test cases automatically from WSDL descriptions. We analyze the web service observability to find the relevant hazards which may be used for testing and those which are always blocked by SOAP processors. We show that few hazards can be really handled. By reducing them, we reduce the test cost too.We improve the robustness issue detection by separating the SOAP processor behavior from the web service one.With an academic tool, we show that many web services have robustness issues and that our method is able to detect them.