Testing is one of the most widely used techniques to increase the quality and reliability of complex software systems. In this paper we present the notion of testing interoperability security rules in virtual organizations. In particular, we incorporate mechanisms to test those interactions among the organizations of the business communities when the resources are shared. In order to apply our technique to increase the confidence on the correctness of these systems, we need to obtain a set of tests compiling the relevant properties of the interoperability security policies. We present a model based testing approach for checking the correctness of these policies in this environment. In addition to provide the theoretical framework, we show how this formalism, based on extended finite automata, has been used to test a hospital scenario. This exercise convinced us that a formal approach to test systems can facilitate some of the development phases. In particular, how to choose which tests to apply, is simplified since tests are automatically extracted from the specification.