The rapid diffusion of Internet and open standard technologies is producing a significant growth of the demand of Web sites and Web applications with more and more strict requirements of usability, reliability, interoperability and security. While several methodological and technological proposals for developing Web applications are coining both from industry and academia, there is a general lack of methods and tools to carry out the key processes that significantly impact the quality of a Web application (WA), such as the validation & verification (V&V), and quality assurance. Some open issues in the field of Web application testing are addressed in this paper. The paper exploits an object-oriented model of a WA as a test model, and proposes a definition of the unit level for testing the WA. Based on this model, a method to test the single units of a WA and for the integration testing is proposed. Moreover, in order to experiment with the proposed technique and strategy, an integrated platform of tools comprising a Web application analyzer, a repository, a test case generator and a test case executor, has been developed and is presented in the paper. A case study, carried out with the aim of assessing the effectiveness of the proposed method and tools, produced interesting and encouraging results.