Environment

Description

I am trying to mock the value returned by a ByRef argument in JustMock. The documentation example for the Matchers page does not use Arg.Ref, which seems to be a mistake. The example is also irrelevant because the mock is based on an interface and there is no original behavior.

I have tried the following method under test:

Public Class SomeDemoClass
    Public Sub SomeByRefParameter(value As String, ByRef out As String)
        out = "Nonsense"
    End Sub
End Class

and the test:

<TestClass>
Public Class UnitTest
    <TestMethod>
    Public Sub ArgRefTest()
        Dim classUnderTest = New SomeDemoClass()
        Dim value = "Hello"
        Dim expectedResult = "The value passed in parameter 'value' is 'Hello'"
        Dim actualResult As String = Nothing

        ' Arrange
        Mock.Arrange(Sub() classUnderTest.SomeByRefParameter(value, Arg.Ref(expectedResult).Value))

        ' Act
        classUnderTest.SomeByRefParameter(value, actualResult)

        ' Assert
        Assert.AreEqual(expectedResult, actualResult)
    End Sub
End Class

The expected result is that actualResult receives the value predefined in expectedResult when the method is called in the Act section. However, actualResult receives the original value instead.

I need to know how to mock the value returned by the ByRef argument.

Solution

To mock the value returned by a ByRef argument in JustMock, you can use the DoInstead arrangement clause. Here is an example code snippet:

<TestClass>
Public Class UnitTest1
    Friend Delegate Sub Overwrite(value As String, ByRef out As String)

    <TestMethod>
    Public Sub ArgRefTest()
        Dim classUnderTest = New SomeDemoClass()
        Dim value = "Hello"
        Dim expectedResult = "The value passed in parameter 'value' is 'Hello'"
        Dim actualResult As String = Nothing

        ' Arrange
        Dim overwrite As Overwrite = Sub(val, ByRef out) out = expectedResult
        Mock.Arrange(Sub() classUnderTest.SomeByRefParameter(value, Arg.Ref(Arg.AnyString).Value)).DoInstead(overwrite)

        ' Act
        classUnderTest.SomeByRefParameter(value, actualResult)

        ' Assert
        Assert.AreEqual(expectedResult, actualResult)
    End Sub
End Class

Please note that the value passed for the ByRef argument is used for matching, which determines whether to apply the arrangement or call the original code.

Notes

• The example in the documentation will be fixed based on your feedback.
• We appreciate your suggestion to add examples and downloadable code to the JustMock API documentation.

See Also

• Matchers Documentation
• JustMock API