FraukeN

    public OverviewPage()
    {
        InitializeComponent();
        IRepository<ToDoItem> repo = SimpleIoc.Default.GetInstance<IRepository<ToDoItem>>();
        _viewModel = new OverviewVM(repo);
        BindingContext = _viewModel;
    }

FraukeN

    public App()
    {
        InitializeComponent();

        SimpleIoc.Default.Register<IRepository<ToDoItem>, MockRepository>();

        MainPage = new OverviewPage();
    }

FraukeN

    [Test]
    public async Task LoadData_sets_IsFaulted_to_true_if_LoadData_encounters_an_exception()
    {
        // Arrange
        Mock<IRepository<ToDoItem>> repoMock = new Mock<IRepository<ToDoItem>>();
        repoMock.Setup(repo => repo.GetAsync()).ThrowsAsync(new Exception());

        OverviewVM vm = new OverviewVM(repoMock.Object);

        // Act

FraukeN

    public OverviewVM(IRepository<ToDoItem> toDoRepo)
    {
        _toDoRepo = toDoRepo ?? throw new ArgumentNullException("toDoRepo");
        IsFaulted = false;
        ErrorMessage = string.Empty;
    }

    public async Task LoadData()
    {
        try

FraukeN

    private bool _isFaulted;
    public bool IsFaulted
    {
        get { return _isFaulted; }
        set { Set(ref _isFaulted, value); }
    }

    private string _errorMessage;
    public string ErrorMessage
    {

FraukeN

    public async Task LoadData_loads_data_from_repository()
    {
        // Arrange
        List<ToDoItem> toDoList = new List<ToDoItem>();
        for (int i = 0; i < 5; i++)
        {
            toDoList.Add(new ToDoItem { Title = $"Item {i}" });
        }
        Mock<IRepository<ToDoItem>> repoMock = new Mock<IRepository<ToDoItem>>();
        repoMock.Setup(repo => repo.GetAsync()).ReturnsAsync(toDoList);

FraukeN

    public OverviewPage()
    {
        InitializeComponent();
        _viewModel = new OverviewVM(null);
        BindingContext = _viewModel;
    }

FraukeN

    [Test]
    public void creating_a_new_instance_of_OverviewVM_with_null_repository_throws_ArgumentNullException()
    {
        // Assert
        Assert.That(() => new OverviewVM(null),
            Throws.Exception
                .TypeOf<ArgumentNullException>()
                .With.Property("ParamName")
                .EqualTo("toDoRepo"));
    }

FraukeN

    public async Task LoadData_loads_data_from_repository()
    {
        // Arrange
        OverviewVM vm = new OverviewVM(new MockRepository());

        // Act
        await vm.LoadData();

        // Assert
        Assert.That(vm.ToDoItems.Count(), Is.EqualTo(3));

FraukeN

    public OverviewVM(IRepository<ToDoItem> toDoRepo)
    {
        _toDoRepo = toDoRepo ?? throw new ArgumentNullException("toDoRepo");
    }