Testing for a Conformance Relation Based on Acceptance

Although the object-oriented paradigm has been gaining wide popularity in recent years, little work has been done on how to test objectoriented software systems. We believe that many special programming features found in the object-oriented paradigm will also play important roles during the testing phase. In this paper, we propose a conformance testing method for object-oriented software systems. The conformance relation that can be tested by this method is based on a modified version of the acceptance tree model and takes into account the special requirements imposed by the inheritance mechanism -which we believe is the most important feature provided by the object-oriented paradigm. The proposed method allows us to test, under certain assumptions, whether an object instance implementation conforms to a given class specification by applying to the implementation the test cases derived from the given class specification. 1 I n t r o d u c t i o n With the increasing complexity of software systems, stepwise refinement is becoming an important methodology for software development. The stepwise refinement approach starts from a formal specification of the functionality of the system on a high level of abstraction. This abstract initial specification is then transformed in a number of successive refinement or implementation steps, where each step produces a new specification reflecting certain design decisions. The transformation process terminates when a physical realization of the system is obtained. With such an approach, implementation and specification only have relative meanings. A refinement produced in an intermediate step is an implementation of the refinement in the previous step, while it also serves as a specification for the refinement in the next step. The stepwise development process must be such that the final realization, as well as the intermediate refinements, conform to the initial specification. Certainly, some criterion should be designated beforehand for specifying the meaning and conditions of "conform". Actually, there have been many criteria proposed for defining possible conformance relationships, such as trace preorder, reduction, extension and conformance of [5, 6, 7],failure of [9, 10], and failure trace and generalized failure of [12]. These relations have been proposed largely for conformance testing of distributed systems, particularly of communication protocols. * This research was supported by a grant from the Canadian Institute for Telecommunications Research under the NCE program of the Government of Canada.