Context independent unique state identification sequences for testing communication protocols modelled as extended finite state machines

Abstract

A number of test sequence generation methods proposed for communication protocols represented as Extended Finite State Machines (EFSMs) use state identification sequences for checking the states. However, neither a formal definition nor a method of computation of these sequences for an EFSM state is known. In this paper, we first define a new type of state identification sequence, called Context Independent Unique Sequence (CIUS) and present an algorithm for computing it. To demonstrate the usefulness of these sequences, we then briefly describe a unified method based on CIUSs for automatically generating executable test cases for both control flow and data flow aspects of an EFSM. In control flow testing, CIUSs are very useful in confirming the tail states of the transitions. In data flow testing, CIUSs improve the observability of the test cases for the def-use associations of different variables used in the EFSM. Unlike general state identification sequences, the use of CIUSs does not increase the complexity of the already intractable feasibility testing problem in test case generation. Moreover, the feasibility problem encountered in both the CIUS computation and the test case generation methods is amenable to an incremental solution. We demonstrate this by presenting a method to solve a particular case of this problem in which the variables are of only integer, real or Boolean type and the predicates are linear.