Add unit tests for BasketService edge cases and multi-item scenarios

tests/Basket.UnitTests/BasketServiceTests.cs

@@ -59,4 +59,83 @@ public async Task GetBasketReturnsEmptyForInvalidUserId()
         Assert.IsInstanceOfType<CustomerBasketResponse>(response);
         Assert.AreEqual(response.Items.Count(), 0);
     }
+
+    [TestMethod]
+    public async Task GetBasketReturnsEmptyWhenRepositoryReturnsNull()
+    {
+        // Arrange: Mock IBasketRepository.GetBasketAsync to return null for a valid user ID
+        var mockRepository = Substitute.For<IBasketRepository>();
+        mockRepository.GetBasketAsync("1").Returns(Task.FromResult<CustomerBasket>(null));
+        var service = new BasketService(mockRepository, NullLogger<BasketService>.Instance);
+        var serverCallContext = TestServerCallContext.Create();
+        var httpContext = new DefaultHttpContext();
+        httpContext.User = new ClaimsPrincipal(new ClaimsIdentity([new Claim("sub", "1")]));
+        serverCallContext.SetUserState("__HttpContext", httpContext);
+
+        // Act: Call GetBasket with a valid user context
+        var response = await service.GetBasket(new GetBasketRequest(), serverCallContext);
+
+        // Assert: The response is a CustomerBasketResponse with zero items
+        Assert.IsInstanceOfType<CustomerBasketResponse>(response);
+        Assert.AreEqual(0, response.Items.Count());
+    }
+
+    [TestMethod]
+    public async Task GetBasketHandlesRepositoryExceptionGracefully()
+    {
+        // Arrange: Mock IBasketRepository.GetBasketAsync to throw an exception for a valid user ID
+        var mockRepository = Substitute.For<IBasketRepository>();
+        mockRepository.GetBasketAsync("1").Returns<Task<CustomerBasket>>(x => throw new Exception("Repository error"));
+        var service = new BasketService(mockRepository, NullLogger<BasketService>.Instance);
+        var serverCallContext = TestServerCallContext.Create();
+        var httpContext = new DefaultHttpContext();
+        httpContext.User = new ClaimsPrincipal(new ClaimsIdentity([new Claim("sub", "1")]));
+        serverCallContext.SetUserState("__HttpContext", httpContext);
+
+        // Act: Call GetBasket with a valid user context
+        // Assert: The service throws the exception (current implementation behavior)
+        await Assert.ThrowsExactlyAsync<Exception>(async () =>
+        {
+            await service.GetBasket(new GetBasketRequest(), serverCallContext);
+        });
+    }
+
+    [TestMethod]
+    public async Task GetBasketReturnsMultipleItemsForValidUserId()
+    {
+        // Arrange: Mock IBasketRepository.GetBasketAsync to return a CustomerBasket with multiple BasketItem objects
+        var mockRepository = Substitute.For<IBasketRepository>();
+        List<BasketItem> items = [
+            new BasketItem { Id = "item-1", ProductId = 1, ProductName = "Product 1", Quantity = 2, UnitPrice = 10.50m },
+            new BasketItem { Id = "item-2", ProductId = 2, ProductName = "Product 2", Quantity = 1, UnitPrice = 25.00m },
+            new BasketItem { Id = "item-3", ProductId = 3, ProductName = "Product 3", Quantity = 3, UnitPrice = 5.75m }
+        ];
+        mockRepository.GetBasketAsync("1").Returns(Task.FromResult(new CustomerBasket { BuyerId = "1", Items = items }));
+        var service = new BasketService(mockRepository, NullLogger<BasketService>.Instance);
+        var serverCallContext = TestServerCallContext.Create();
+        var httpContext = new DefaultHttpContext();
+        httpContext.User = new ClaimsPrincipal(new ClaimsIdentity([new Claim("sub", "1")]));
+        serverCallContext.SetUserState("__HttpContext", httpContext);
+
+        // Act: Call GetBasket with a valid user context
+        var response = await service.GetBasket(new GetBasketRequest(), serverCallContext);
+
+        // Assert: The response contains the correct number of items and the expected item details
+        Assert.IsInstanceOfType<CustomerBasketResponse>(response);
+        Assert.AreEqual(3, response.Items.Count());
+
+        var itemsList = response.Items.ToList();
+
+        // Verify first item details
+        Assert.AreEqual(1, itemsList[0].ProductId);
+        Assert.AreEqual(2, itemsList[0].Quantity);
+
+        // Verify second item details
+        Assert.AreEqual(2, itemsList[1].ProductId);
+        Assert.AreEqual(1, itemsList[1].Quantity);
+
+        // Verify third item details
+        Assert.AreEqual(3, itemsList[2].ProductId);
+        Assert.AreEqual(3, itemsList[2].Quantity);
+    }
 }