An User-Oriented Testing of Real Time Systems

This paper presentsa technique to testing real-time systems thr ough the derivation of executabletest casesfr om test purposes(express user properties) on a specification,modelled as a timed automaton. The study dealswith an equivalent representationof timed automata: clock region graphs. A test purposeis an acyclic graph, all paths of this graphs which are found on the specificationwill be considered asa test case.The timing constraints of both the specificationand the test purposeshould be the same.Wewill alsoshow how to executethe derived testcaseson the implementation thr ough a dedicatedtest architecture. This executionallows both to discriminate betweenthe different cases(input, output or waiting) and to testa representati ve part of the infinite setof clock values.Finally, a simpleexampleillustrates the useof this technique. Keywords— Real-Time, Timed Automata, Region Graph, Conformance Testing,Testpurpose. I . INTRODUCTION N the software and hardware designprocess,conformance testingis a very importantstepandcostsa lot of money: it shows the confidencelevel we can have about implementing any systemspecification.Sincetime is obviously a crucial feature for timed systems(multimediaprotocols,embeddedsystems,air traffic systems)it hasto be taken into accountin the testingsteps. This study dealswith timed systemsdescribed as Input Output Timed Automata(definedas automatawhere eachtransitioncanbeareitheran input actionor outputaction andsometimestiming constraints),widely usedin theprotocol engineeringarea. In this field, we usuallydealwith two main validationtechniques: the verificationapproach, which handlesthe systemspecificationandtriesto prove its correctness(in this casethesystem is a white box). Usually, the userpropertiesareexpressedby anotherformalismas temporallogics andmustbe verified on thespecificationby usinga model-checkerfor example, the testingapproach, which usesthe implementationof the systemandtriesto find any faulty behavior in it without having apriori any informationaboutthestructureof thesystem(in this casethe systemis a black box). The testgenerationproduces sequences of inputs(actions)from thespecification,andtheimplementationmust be able to executethesesequences(called ’ testsequences’ ) andto answerwith theexpectedoutputs. This study focuseson the secondtechnique,and expresses timed systemsby meansof modelsuponwhich we canapply classicaltechniques, suchasthederivationof testpurposesand the constructionof a canonicaltester . We developa technique describingthe test executionprocessand taking into account boththenatureof theactionstobeperformedandthetimewhere they shouldbeperformed. Thispaperis organizedasfollows: section2 recallssomepreviouswork on timedtesting.Section3 providesthetheoretical basisof our study. Section4 developsour testgenerationtechniquefrom timed testpurposes.Section5 concentrateson the LERI-RESYCOMUniversit́e de ReimsChampagne-Ardenne, UFR Sciences Exacteset Naturelles,Moulin de la Housse,BP 1039,51687ReimsCedex 2, France,e-mail:Hacene.F ouchal,Eric.Petitjean,Sebastien.Salv a@uni v-reims.fr algorithmsof testexecutionanda testarchitecturededicatedto timedsystemstesting.Finally, section6 concludesandpresents someextensionsto our work.