Mocking FBs - Manual - AxUnit-ST - AxUnit ST documentation package - AxUnit-ST,

AxUnit-ST CLI Tool (test)
Portfolio
SIMATIC AX
Product
AxUnit-ST
Software version
8.0.33
Edition
04/2025
Language
English (original)
Package Name
@ax/axunitst-docs

In the following example, we demonstrate how to test a function which depends on System.Counter.

Again we use Dependency Injection to abstract from the concrete implementation of the system function:

INTERFACE PUBLIC ICount
    METHOD CounterImpl : LINT
    END_METHOD
END_INTERFACE

This is the implementing class:

CLASS PUBLIC CountImpl IMPLEMENTS ICount

    VAR PUBLIC
        MySystemCounter : System.Counters.Counter;
    END_VAR
    METHOD PUBLIC CounterImpl : LINT
        VAR_TEMP
            value : LINT;            
        END_VAR

        MySystemCounter();
    END_METHOD
END_CLASS

Let the class under test use the interface ICount, so that the class is independent of the system implementation.

CLASS UsingCounterImpl 

    VAR PUBLIC
        Count : ICount;       
    END_VAR 

    METHOD PUBLIC CountedEnough : BOOL

        VAR_TEMP
            myValue : LINT;
        END_VAR 

        myValue := Count.CounterImpl();


        IF myValue > 9 THEN
            CountedEnough := TRUE;
        ELSE
            CountedEnough := FALSE;
        END_IF;

    END_METHOD
END_CLASS

Writing the mock now enables you to control the output variable of the FB. Here it is set to the value of the input variable:

CLASS PUBLIC CountMock IMPLEMENTS ICount

    VAR PUBLIC
        MySystemCounter : CounterFB_Mock;
    END_VAR
    METHOD PUBLIC CounterImpl : LINT
        VAR_TEMP
            value : LINT;            
        END_VAR

        MySystemCounter();
    END_METHOD
END_CLASS

// Here you can control your value
FUNCTION_BLOCK CounterFBMock
    VAR_INPUT
        valueToSet : LINT;
    END_VAR

    VAR_OUTPUT
        value : LINT;
    END_VAR

    value := valueToSet;

END_FUNCTION_BLOCK

Finally, you can write your test: 

   {TestFixture}
    CLASS MyTestFixture
        VAR
            _myVar : UsingCounterImpl;
            _myMock : CountMock;
        END_VAR

        {Test}
        METHOD PUBLIC MyTestMethod

            _myVar.Count := myMock;
            _myMock.MySystemCounter.valueToSet := 10;
            Assert.Equal(_myVar.CountedEnough(), TRUE);
        END_METHOD
    END_CLASS