The selection of appropriate test cases is an important issue for conformance testing of protocol implementations as well as in software engineering. A number of methods are known for the selection of a test suite based on the specification of the implementation under test, assumed to be given in the form of a finite state machine. This paper presents a new method which provides a logical link between several of the known methods. Called "partial W method", it has general applicability, full fault detection power, and yields shorter test suites than the W method. The second part of the paper discusses various other issues which have an impact on the selection of a suitable test suite. This includes the consideration of interaction parameters, various test architectures for protocol testing, and the fact that many specifications do not satisfy the assumptions made by most test selection methods, such as complete definition, a correctly implemented reset function, a limited number of states in the implementation, and determinism.

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Systematic test sequence generation for communication protocols in conformance testing has been an active research area during the last &c&. Methods were developed to produce optimized test sequences for detecting faults in an implementation under test (IUT). However, the application of these methods gives only limited information about the locations of detected faults. Therefore, we propose a complementary step which localizes the faulty transition in a deterministic finite state machine (FSM) once the fault has been detected. A diagnostic algorithm will generate, if necessary, additional diagnostic test cases which depend on the observed symptom and which permit the location of the detected fault. The algorithm guarantees the diagnostic of any single (output or transfer) fault in an FSM. An application example, explaining the functioning of the algorithm, is provided in the paper.

In this paper, we propose a generalized diagnostic algorithm for the case where more than one fault (output a d o r transfer) may be present in the transitions of a system represented by a deterministic finite state machine (FSM). If existing faults are detected, this algorithm permits the generation of a minimal set of diagnoses, each of which is formed by a set of transitions (with specific types of faults) suspected of being faulty. The occurrence in an implementation, of all the faults of a given diagnosis, allows the explanation of all observed implementation outputs. The algorithm guarantees the correct alagnosis of certain conjigurations of faults (output a d o r transfer) in an implementation, which are characterized by a certain type of independence of the different faults. We also propose an approach for selecting additional test cases, which allows the reduction of the number of possible diagnoses. A simple example is used to demonstrate the different steps of the algorithm

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