The increasing diffusion and importance of Web Applications has led to strict requirements in terms of continuity of the service, because their unavailability can lead to severe economic losses. Techniques to assure the quality of these applications are thus needed in order to identify in advance possible faults. Model-driven approaches to the testing of Web Applications can provide developers with a way of checking the conformance of the actual Web Application with respect to the model built from the requirements. These approaches can be used to automatically generate from the model a set of test cases satisfying certain coverage criteria, and thus can be integrated in a classical test driven development process. In this paper we present an automated technique for Web Application testing using a model-driven approach. We present a way of modeling Web Applications by Abstract State Machines (ASMs), and a process for generating automatically from the model a concrete test suite that is executed on the Web Application under test in order to check the conformance between the application and the model.