EETimes

Embedded Systems October 2000 Vol13_11

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a. go 5' /D FIGURE 1 Emulation of domain's target environment ------- Test Driver - Emulates both client and server domains (with respect to the domain under test) ----- "-----='- - --- .--- Service Invocations Stubbed Service Calls : · · , · , , Domain Under Test '-. - ...... interfacing."2 UML models and object- oriented software tend to have classes with many complex interactions, which hinder integration testing. Combining a stmctured approach to UML analysis modeling with a coherenL integration and test strategy will make developing quality embedded systems easier. A software faul t is an erroneous instruction or computation within a p.-ogram. Executio n of that fa ult results in an erro r in the state of the software. \""hen the error is propagat- ed to the output, and becomes visible outside the system as an unexpected result, a fa ilure has occurred. Controllability of a program is the abili- ty of a suite of test cases to force dle program under test to follow a partic- ular execution path, possibly execut- ing faul ts along dle way. Obseroabilityof a p.-ogram is the abili ty of the test suite to detect an error state, and thereby illuminate the existence of a fault. The internal state of the system is impo rtant in determining the correct- ness of tests. The output of a system is .. ...... -' - .- dependent upon bodl dle initial state of dle system and dle inputs applied to it. The same set of inputs applied to a different initial state will result in dif- ferent outputs. The flnal state of the system must also be examined as part of evaluating the cOlTectness of the test, as an incorrect internal state may evntually propagate to the system out- put, cau ing a failure_ System complex- ity may also make it difficult to predict dle correct outputs of the system. Initial State + In1JuiS - > Final State + OutpUIS Using black box test techniques, only the external inputs and o utputs of dle system are available. A distinguish- ing sequence of test stimuli is required to propagate an error to the output so as to distinguish a faul ty program from a correct one. The longer the required di stinguishing sequence, th e less testable the program. Embedded sys- tems are similar to black boxes in that controllabili ty and observability are 140 OCTOBER 2000 Embedded Systems Programming . . , --- .................. Obj1 .. - ...... --. usually limi ted. Evaluating the fi nal internal state of the system resul ts reduces the distinguishing sequence of inputs required to detect an error, resulting in smaller, more manageable test cases. Instrumentation seeks to in crease both controllabili ty and observability in a so[tw

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