A passive testing approach based on invariants: application to the WAP

摘要

This paper presents a new methodology to perform passive testing based on invariants. This novel approach is supported by the following idea: a set of invariants represent the most relevant expected properties of the implementation under test. Intuitively, an invariant expresses the fact that each time the implementation under test performs a given sequence of actions, then it must exhibit a behavior reflected in the invariant. For example, an invariant such as i_1/ o_1,...,i_(n-1)/o_(n-1),i_n/O must be interpreted as "each time the implementation performs the sequence i_1/o_1,...,i_(n-1)/o_(n-1),i_n the next observed output belongs to the set O". We call these invariants simple invariants. In this work we introduce a new notion of invariants to deal with more subtle properties. For instance, we will consider invariants to express properties such as "if y happens then we must have that x had happened before". These invariants are called obligation invariants. We present algorithms to decide the correctness of the proposed invariants with respect to a given specification. Once we have that an invariant is correct with respect to a given specification, we check whether the execution traces observed from the implementation respect the invariant. In order to perform this phase we present two algorithms based, respectively, on left-to-right and right-to-left pattern matching algorithms. In addition to the theoretical framework we have developed a software tool, called TESTINV, that helps in the automation of our passive testing approach. In particular, the algorithms presented in this paper are fully implemented in the tool. Finally, in order to test the usefulness of our approach we have chosen a real-life case study: the Wireless Application Protocol (WAP). We present a test architecture as well as the most relevant results obtained from the application of our approach to the WAP.