Improving Coverage Based Test Purposes

Test purposes have been presented as a solution to avoid the state space explosion when selecting test cases from formal models. We previously presented a technique that assists a test engineer with test purpose design: It allows automatic generation of coverage based test suites and can be used to automatically exercise those aspects of the system that manually designed test purposes missed. Although the generated test purposes allow for coverage based testing, they did not comprise refuse states. Refuse states in test purposes restrict the state space that needs to be considered during test case generation. In this paper, we present an approach that leads to test purposes with refuse states, thus speeding up the test case generation. Furthermore, our new approach allows one to generate test cases for coverage items where our previous approach failed. We consider coverage of LOTOS specifications, and show how data flow graphs help to improve coverage based test purposes. We then show how existing tools can be used to efficiently derive test cases and present first experimental results.