How to mock DragEventArgs

Question

I am trying to unit test this method that is called from my ViewModel:

  public virtual string[] ExtractFilePaths(DragEventArgs dragEventArgs)
  {
     string[] droppedPaths = null;

     if (dragEventArgs.Data.GetDataPresent(DataFormats.FileDrop))
     {
        droppedPaths = dragEventArgs.Data.GetData(DataFormats.FileDrop, true) as string[];
     }

     return droppedPaths;
  }

I have this method wired up with Caliburn. I know it's a pretty simple method that almost exclusively uses framework classes, but I feel it still needs testing. The problem is, Moq cannot mock the DragEventArgs. Is there a way around this or should I just not bother testing this method?

Answer 1

Hopefully I am not missing anything with Calibrun, but why mock DragEventArgs when you can create one? The important part is the IDataObject part, which is an interface and can easily be mocked.

[Test]
public void ExtractFilePaths_WithFileDrop_ReturndDropPaths()
{
    var fileList = new[] {@"c:\path\path\file1.txt", @"d:\path2\path2\file2.txt"};
    var stubData = Mock.Of<IDataObject>(x =>
                                        x.GetDataPresent(DataFormats.FileDrop) == true &&
                                        x.GetData(DataFormats.FileDrop, true) == fileList);

    var dragEventArgs = new DragEventArgs(stubData, 0, 0, 0, DragDropEffects.Move, DragDropEffects.Scroll);

    var subject = new Subject();

    // Act
    var result = subject.ExtractFilePaths(dragEventArgs);

    // Assert
    Assert.That(result, Is.Not.Null, "Expected array to be returned");
    Assert.That(result, Is.EquivalentTo(fileList));
}

Answer 2

Replace DragEventArgs class with only the data you want to use in your function. DragEventArgs belongs to UI, not ViewModel.