Remove basket items when basket is deleted (#170)

* Proving out removing the basket items at the same time the basket is deleted

* Fixing existing unit tests

* Adding a unit test for the Deletebasket method

* Rename test and deleting basket items before basket

* Added integration test for DeleteAsync method for BasketItems

- Also added a BasketBuilder to create a Basket with no items, or one item.

tests/IntegrationTests/Repositories/BasketItemRepositoryTests/DeleteAsync_Should.cs

@@ -0,0 +1,46 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.eShopWeb.ApplicationCore.Entities.BasketAggregate;
+using Microsoft.eShopWeb.Infrastructure.Data;
+using Microsoft.eShopWeb.UnitTests.Builders;
+using System.Linq;
+using System.Threading.Tasks;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.eShopWeb.IntegrationTests.Repositories.BasketItemRepositoryTests
+{
+    public class DeleteAsync_Should
+    {
+        private readonly CatalogContext _catalogContext;
+        private readonly EfRepository<Basket> _basketRepository;
+        private readonly EfRepository<BasketItem> _basketItemRepository;
+        private BasketBuilder BasketBuilder { get; } = new BasketBuilder();
+        private readonly ITestOutputHelper _output;
+
+        public DeleteAsync_Should(ITestOutputHelper output)
+        {
+            _output = output;
+            var dbOptions = new DbContextOptionsBuilder<CatalogContext>()
+                .UseInMemoryDatabase(databaseName: "TestCatalog")
+                .Options;
+            _catalogContext = new CatalogContext(dbOptions);
+            _basketRepository = new EfRepository<Basket>(_catalogContext);
+            _basketItemRepository = new EfRepository<BasketItem>(_catalogContext);
+        }
+
+        [Fact]
+        public async Task DeleteItemFromBasket()
+        {
+            var existingBasket = BasketBuilder.WithOneBasketItem();
+            _catalogContext.Add(existingBasket);
+            _catalogContext.SaveChanges();
+            
+            await _basketItemRepository.DeleteAsync(existingBasket.Items.FirstOrDefault());
+            _catalogContext.SaveChanges();
+
+            var basketFromDB = _basketRepository.GetById(BasketBuilder.BasketId);
+
+            Assert.Equal(0, basketFromDB.Items.Count);
+        }
+    }
+}