public void ItGetsAllAvailableItems() { //Arrage //Act _checkoutFactory.Setup(x => x.CreateCheckout()).Returns(Mock.Of <List <IItemPriceRule> >); _repo.Setup(x => x.DisplayAvailableItems()).Returns(Mock.Of <List <ProductDto> >); _checkout = new Service.Checkout(_checkoutFactory.Object, _repo.Object); var results = _checkout.DisplayAvailableItems(); //Assert Assert.IsNotNull(results); Assert.IsInstanceOfType(results, typeof(List <Product>)); }