public void CheckoutCommand_NotExecutable_IfNoItemsInCart() { var navigationService = new MockNavigationService(); var shoppingCartRepository = new MockShoppingCartRepository(); shoppingCartRepository.GetShoppingCartAsyncDelegate = () => Task.FromResult<ShoppingCart>(null); var eventAggregator = new MockEventAggregator(); eventAggregator.GetEventDelegate = type => new MockShoppingCartUpdatedEvent(); var target = new ShoppingCartPageViewModel(shoppingCartRepository, navigationService, null, null, null, null, null, null, eventAggregator); target.UpdateShoppingCartAsync(null); Assert.IsFalse(target.CheckoutCommand.CanExecute()); shoppingCartRepository.GetShoppingCartAsyncDelegate = () => Task.FromResult(new ShoppingCart(new Collection<ShoppingCartItem>()){Currency = "USD", FullPrice = 0, TaxRate = 0, TotalDiscount = 0, TotalPrice = 0}); target.UpdateShoppingCartAsync(null); Assert.IsFalse(target.CheckoutCommand.CanExecute()); shoppingCartRepository.GetShoppingCartAsyncDelegate = () => Task.FromResult(new ShoppingCart(new Collection<ShoppingCartItem> { new ShoppingCartItem{Product = new Product(), Currency = "USD", Quantity = 0} }) { Currency = "USD", FullPrice = 0, TaxRate = 0, TotalDiscount = 0, TotalPrice = 0 }); target.UpdateShoppingCartAsync(null); Assert.IsTrue(target.CheckoutCommand.CanExecute()); }