使用 Moq 框架在 WPF MVVM 中测试 ViewModel

Question

I am new to Moq framework. I have a viewmodel with injected IEntityRepository

public class MainViewModel
{
    private readonly IEntityRepository _entityRepository;

    public MainViewModel(IEntityRepository entityRepository)
    {
        _entityRepository = entityRepository;
        Entities = new ObservableCollection<EntityWrapper>();
    }

    public ObservableCollection<EntityWrapper> Entities { get; set; }

    public void Load()
    {
        var entities = _entityRepository.GetAll();

        Entities.Clear();

        foreach (var entity in entities)
        {
            Entities.Add(new EntityWrapper(entity));
        }
    }

    public void AddEntity(string name, int x, int y)
    {
        var entity = new Entity()
        {
            Name = name,
            X = x,
            Y = y
        };
        _entityRepository.AddEntity(entity);
        _entityRepository.Save();
    }
}

and EntityRepository is like this:

public class EntityRepository : IEntityRepository
{
    private Context _context;

    public EntityRepository(Context context)
    {
        _context = context;
    }

    public Entity Get(long id)
    {
        return _context.Entities.Find(id);
    }

    public IEnumerable<Entity> GetAll()
    {
        return _context.Entities.ToList();
    }

    public void AddEntity(Entity entity)
    {
        _context.Entities.Add(entity);
    }

    public void Save()
    {
        _context.SaveChanges();
    }
}

Now, I want to test Load and AddEntity methods of MainViewModel this is my test class:

[TestClass]
public class MainViewModelTests
{
    private Mock<IEntityRepository> _mockRepo;
    private MainViewModel _mainViewModel;

    public MainViewModelTests()
    {
        _mockRepo = new Mock<IEntityRepository>();
        _mainViewModel = new MainViewModel(_mockRepo.Object);
    }

    [TestMethod]
    public void AddEntityTest()
    {
        var entity = new Entity()
        {
            Name = "Student",
            X = 10,
            Y = 20
        };

        _mainViewModel.AddEntity("Student", 10, 20);

        _mockRepo.Setup(m => m.AddEntity(entity));
        _mockRepo.Setup(m => m.Save());

        var entities = _mainViewModel.Entities;
        Assert.AreEqual(1, entities.Count);
    }

    [TestMethod]
    public void LoadTest()
    {
        // How to add fake data???

        _mockRepo.Setup(r => r.GetAll());

        _mainViewModel.Load();

        var entities = _mainViewModel.Entities;
        Assert.AreEqual(1, entities.Count);
    }
}

In AddEntityTest() I don't know why the property Entities will be empty and in LoadTest how to populate fake data so that I can load it.

Answer 1

To get a test data in LoadTest method you can use Moq Returns method

_mockRepo.Setup(r => r.GetAll()).Returns(new List<Entity> { new Entity() });

It works, because List<T> implements IEnumerable<T> .

As for the AddEntityTest , there are a couple of issues here. You setup the mock

_mockRepo.Setup(m => m.AddEntity(entity));
_mockRepo.Setup(m => m.Save());

after _mainViewModel.AddEntity("Student", 10, 20); call. It should come before, Arrange step is always before Act step, according to AAA pattern

You also don't update Entities collection after adding an entity, so the Entities.Count remains the same. I suggest you to setup a IEntityRepository.GetAll() mock as well for this test and update an Entities collection in MainViewModel . Or rewrite the logic of your AddEntityTest , if collection update performed through view