Due to the increasing complexity of distributed systems, security testing is becoming increasingly critical in insuring reliability of such systems in relation to their security requirements. To challenge this issue, we rely in this paper on model based active testing. In this paper we propose a framework to specify security policies and test their implementation. Our framework makes it possible to automatically generate test sequences, in order to validate the conformance of a security policy. This framework contains several new methods to ease the test case generation. To demonstrate the reliability of our framework, we present a Vehicular Networks System as an ongoing case study