You can find several articles about testing state machines, but the one written by Martin Gomez [1] nicely summarizes the usually used approach. “The beauty of coding even simple algorithms as state machines is that the test plan almost writes itself. All you have to do is to go through every state transition. I usually do it with a highlighter in hand, crossing off the arrows on the state transition diagram as they successfully pass their tests. This is a good reason to avoid "hidden states"-they're more likely to escape testing than explicit states. Until you can use the "real" hardware to induce state changes, either do it with a source-level debugger, or build an "input poker" utility that lets you write the values of the inputs into your application.” Written in 2000 this still describes the common practice. In the following text I’ll show how the sinelabore codegenerator can support you in testing state machines. Furthermore a waveform viewer is suggested to display the test results. The latest beta version of the codegenerator automatically finds and prints ways through a given state chart. The algorithm ensures that all transitions are taken at least once (100% coverage). So it is not anymore necessary to go through the diagram with a highlighter in hand. Depending on the complexity of the machine not a single way can cover all transitions but several ways are necessary starting from different states. The following command creates the state machine code from the equivalent.xml specification (see example 1). In addition it prints out one or more routes to test the state machine. The new command line option ‘-c’ switches on the path coverage output.
 java -jar ../../../testcases/codegen.jar -v -c -p md -o equivalent -t "Model:Equivalent" equivalent.xml The output looks the following../../../../PLC_Open_Saftey_Block.html../../../../PLC_Open_Saftey_Block.htmlshapeimage_3_link_0shapeimage_3_link_1

Figure 3: Waveform view for the test pattern data testpatternCoverage1to8. The first seven signals show the inputs and outputs of the machine. The last two signals show the active top level state (RootLevel) and the active child state within the Active state.


It’s quite simple to create such a diagram. The wave viewer is based on styx which was developed from the university of Hamburg / Germany. A little piece of C-code (see end of the article) creates the required input file which is then displayed from the waveform viewer. This works without any further help if the test-bed is running on a PC.


If you run the state machine on the target hardware this is usually not that simple anymore. But there might be a serial interface left that allows you to send the required data (in a compact format) to the PC. On the PC side a small tool is then needed to write the received data to a file.

The updated test driver would then look this:


// select test data

pTestdata = testpatternCoverage1to8;

size=sizeof(testpatternCoverage1to8)/sizeof(IO_DATA);

char buffer[20]={0};


do {


    // dump inputs here

updateTime(testpatternIdx);

startItem();// start a new data set

sprintf(buffer,"%d",getEnable());

addItemAttribute("Enable",buffer);

sprintf(buffer,"%d",getS_ChannelA());

addItemAttribute("A",buffer);

sprintf(buffer,"%d",getS_ChannelB());

addItemAttribute("B",buffer);


equivalent(&instData);// execute generated state machine


// dump outputs and state

sprintf(buffer,"%d",getReady());

addItemAttribute("Ready",buffer);

sprintf(buffer,"%d",getS_EquivalentOut());

addItemAttribute("Out",buffer);

sprintf(buffer,"%d",getError());

addItemAttribute("Error",buffer);

sprintf(buffer,"%d",getDiag());

addItemAttribute("Diag",buffer);

addItemAttribute("RootLevel",states[instData.stateVar]);

addItemAttribute("InnerActive",states[instData.stateVarActive]);

endItem();// end of data set


    testpatternIdx++;     // next test pattern

    if (testpatternIdx == size)// end?

        shouldStop=1;

}while(shouldStop==0);


To display the stored waveform just type java -jar scviewer.jar testpatternCoverage1to8.xml showing the waveform.


This article has discussed how to test state machines and how the sinelabore codegenerator and a waveform viewer can support you. I hope this article was useful for you. And as usual is your feedback very welcome!


The files mentioned in the article are available here:

The source for the waveform viewer can be provided on request. Styx/hades can be downloaded here.


[1] Martin Gomez, Embedded.com, 12/2000

 

Figure 2: State machine with test path from step 0 to 8 as suggested from the coverage algorithm.

Figure 1: Coverage output generated from the code generator for the equivalent state machine.