This paper provides the basis for integrating the Software Cost Reduction (SCR) specification method with the T-VEC (Test VECtor) test vector generator and specification analysis system. The SCR model is mapped to the T-VEC model to support automatic test vector generation for SCR specifications. The T-VEC system generated test vectors for an example SCR specification that was translated into the T-VEC language. The relationships between the models and the resulting test vectors are described. Two general guidelines for the translation process were identified that are fundamental for testing specifications that use event operators and for structuring the specifications to provide tests for all specified requirements. T-VEC is an integrated development environment and associated specification and verification method [BB96]. It was used to develop two avionics systems that were certified by the Federal Aviation Administration (FAA) based on DO-178A-Software Considerations in Airborne Systems and Equipment Certification [RTCA92] (now DO-178B). These certification guidelines emphasize a software engineering approach, where requirement-based testing and analysis are key to supporting the assurance arguments required for certification. One of the key tools of the T-VEC system is an automatic test vector generator; it determines test Copyright (c) 1997 Institute of Electrical and Electronics Engineers. Reprinted, with permission, from the Proceedings of COMPASS 97.
This paper describes the application of the Test Automation Framework (TAF) on the Mars Polar Lander (MPL) software. The premature shutdown of the descent engine on the MPL spacecraft is believed to be the most likely cause for the mission failure. It is believed that the engine shutdown occurred when the three landing legs were extended into their deployed position. This event created an unanticipated transient touchdown indication from the legs, causing the software to inadvertently shutdown the descent engines prior to reaching the surface of Mars. This spurious indication should have been ignored by the Touchdown Monitor (TDM) software, but due to a design flaw, was actually "latched," thus causing the premature engine shutdown. The TAF approach was used to model the TDM software requirements. The associated TAF tools generated tests that identified a potential TDM fault.
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