How to test region manager navigation with Unit tests and Prism 6 (WPF & MVVM)

Question

I have a view model that contains a list of algorithms. The list is displayed in the View as a ListBox and the user can select one of the algorithms. After an algorithm is selected, the user can click on a button that should execute a command in the view model that loads a different view, with the selected algorithm's details.

I want to test this by creating an unit test and assuring that the navigation works as well. But I guess I need to do some extra initialization for the region manager, because the IRegionManager.Regions collection is null and since it is read-only, I cannot create it.

[TestClass]
public class MockingAlgorithmsTests
{
    [TestMethod]
    public void AlgorithmVM_LoadSelectedAlgorithmCommand()
    {
        Mock<IRegionManager> regionManagerMock = new Mock<IRegionManager>();
        Mock<IEventAggregator> eventAgregatorMock = new Mock<IEventAggregator>();
        IAlgorithmService algorithmService = new MockingAlgorithmService();

        AlgorithmsViewModel algorithmsVM = new AlgorithmsViewModel(regionManagerMock.Object, eventAgregatorMock.Object, algorithmService);

        // select algorithm
        algorithmsVM.SelectedAlgorithm = algorithmsVM.Algorithms.First();
        // execute command which uses the previous selected algorithm
        // and navigates to a different view
        algorithmsVM.LoadSelectedAlgorithmCommand.Execute(null);

        // check that the navigation worked and the new view is the one 
        // which shows the selected algorithm
        var enumeratorMainRegion = regionManagerMock.Object.Regions["MainContentRegion"].ActiveViews.GetEnumerator();
        enumeratorMainRegion.MoveNext();
        var viewFullName = enumeratorMainRegion.Current.ToString();
        Assert.AreEqual(viewFullName, "TestApp.AlgorithmViews.AlgorithmDetails");
    }
}

This is the test, any suggestion would be helpful. Thank you, Nadia

Answer 1

I was facing same issue for sometime, then I have mocked everything which was needed to region manager. Please see below code snippet if this helps you.

var regionManager = new Mock<IRegionManager>();     
var navigationJournal = new Mock<IRegionNavigationJournal>();
                navigationJournal.Setup(x => x.GoBack()).Callback(() =>
                {
                   // Verify back operation performed
                });
    
var regionNavigationService = new Mock<IRegionNavigationService>();
                regionNavigationService.Setup(x => x.Journal).Returns(navigationJournal.Object);
    
var navRegionMock = new Mock<IRegion>();
                navRegionMock.Setup(x => x.NavigationService).Returns(regionNavigationService.Object);
                regionManager.SetupGet(x => x.Regions[RegionNames.ShellContentRegion]).Returns(navRegionMock.Object);