public void Test_Update_WithNonExistingList() { //Arrange var controller = new ListsController(listService); var updatedList = new ToDoList { Id = "3", Name = "Test Code", Items = new List <Item> { new Item { Id = 0, Name = "Arrange", IsChecked = true }, new Item { Id = 1, Name = "Act", IsChecked = true }, } }; //Act var result = controller.Update(updatedList) as NotFoundResult; //Assert Assert.IsInstanceOfType(result, typeof(NotFoundResult)); Assert.AreEqual(result.StatusCode, 404); listService.DidNotReceive().Update("3", updatedList); }