Checking that CancellationTokenSource.Cancel() was invoked with Moq

Question

I have a conditional statement which should looks as follows:

//...
if(_view.VerifyData != true)
{
    //...
}
else
{
    _view.PermanentCancellation.Cancel();
}

where PermanentCancellation is of type CancellationTokenSource.

Im wondering how i should set this up in my mock of _view. All attempts thus far have failed :( and i cant find an example on google.

Any pointers would be appreciated.

Answer 1

Because CancellationTokenSource.Cancel is not virtual you cannot mock it with moq.

You have two options:

Create a wrapper interface:

public interface ICancellationTokenSource
{
    void Cancel();
}

and an implementation which delegates to the wrapped CancellationTokenSource

public class CancellationTokenSourceWrapper : ICancellationTokenSource
{
    private readonly CancellationTokenSource source;

    public CancellationTokenSourceWrapper(CancellationTokenSource source)
    {
        this.source = source;
    }

    public void Cancel() 
    {
        source.Cancel();
    }

}

And use the ICancellationTokenSource as PermanentCancellation then you can create an Mock<ICancellationTokenSource> in your tests:

// arrange

var mockCancellationTokenSource = new Mock<ICancellationTokenSource>();
viewMock.SetupGet(m => m.PermanentCancellation)
        .Returns(mockCancellationTokenSource.Object)

// act

// do something

// assert

mockCancellationTokenSource.Verify(m => m.Cancel());

And use the CancellationTokenSourceWrapper in your production code.

Or use a mocking framework which supports mocking non virtual members like:

• Microsoft Fakes
• Typemock isolator (commercial)
• JustMock (commercial)