Fast Testing of Critical Properties through Passive Testing

We present a novel methodology to perform passive testing. The usual approach consists in recording the trace produced by the implementation under test and trying to find a fault by comparing this trace with the specification. We propose a more active approach to passive testing where the minimum set of (critical) properties required to a correct implementation may be explicitly indicated. In short, an invariant expresses that each time that the implementation under test performs a given sequence of input/output actions, then it must show a behavior reflected in the invariant. By using an adaptation of the classical pattern matching algorithms on strings, we obtain that the complexity of checking whether an invariant is fulfilled by the observed trace is in O(n · m), where n and m are the lengths of the trace and the invariant, respectively. If the length of the invariant is much smaller than the length of the trace then this complexity is almost linear with respect to the length of the trace. Actually, this is usually the case for most practical examples. In addition to our methodology, we present the case study that was the driving force for the development of our theory: The Wireless Application Protocol (WAP). We present a test architecture for WAP as well as the experimental results obtained from the application of our passive testing with invariants approach.