No abstract

Abstract-In this paper, we consider a test derivation strategy for testing protocol implementations based on Finite State Machines with timeouts. The strategy is applied for testing TFTP implementations. Keywords-Finete State Machine (FSM); FSM with timeouts (timed FSM); transition tour I.INTRODUCTION FSM-based test derivation strategies for conformance testing of protocol implementations are well known [see, for example, 1-3] and a number of formal methods were developed for deriving tests which check time constraints of a discrete event system implementation. Some of them use FSM-based strategies for test derivation [4][5][6][7][8][9][10][11]. One of such strategies uses the model of a timed FSM (TFSM) with so-called timeouts [7][8][9][10][11], i.e., if no input is applied during an appropriate time period the FSM can move to another prescribed state. Correspondingly, the behavior of an FMS significantly depends on a time instance when an input is applied, i.e., the behavior of the FSM is specified for timed input sequences. In [12], it is shown how this behavior can be described by an ordinary FSM with an additional input symbol (a time unit) and thus, despite of the fact that a test suite derived for such an abstract FSM using black-box testing methods returns highly redundant tests, FSM-based test derivation methods can be directly used when deriving tests from an FSM with timeouts. In this paper, we derive a test suite as a transition tour of an appropriate FSM, since W-based testing methods [3] ask for the specification FSM to be complete and deterministic and this usually does not hold for FSMs which describe protocol behavior. We then analyze the fault coverage of a transition tour for TFTP (Trivial File Transfer Protocol) [13] implementations where the behavior significantly depends on timeouts. The contributions of the paper can be summarized as below.