Added test and minor fix

Author: Usik2203

app/code/Magento/QuoteGraphQl/Model/CartItem/DataProvider/UpdateCartItems.php

@@ -64,8 +64,11 @@ public function __construct(
      *
      * @param Quote $cart
      * @param array $items
+     *
      * @throws GraphQlInputException
      * @throws LocalizedException
+     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
+     * @SuppressWarnings(PHPMD.NPathComplexity)
      */
     public function processCartItems(Quote $cart, array $items): void
     {

dev/tests/api-functional/testsuite/Magento/GraphQl/Quote/Guest/UpdateCartItemsTest.php

@@ -7,8 +7,9 @@
 
 namespace Magento\GraphQl\Quote\Guest;
 
-use Magento\Quote\Model\QuoteFactory;
+use Exception;
 use Magento\Catalog\Api\ProductRepositoryInterface;
+use Magento\Quote\Model\QuoteFactory;
 use Magento\Quote\Model\QuoteIdToMaskedQuoteIdInterface;
 use Magento\Quote\Model\ResourceModel\Quote as QuoteResource;
 use Magento\TestFramework\Helper\Bootstrap;
@@ -273,6 +274,81 @@ private function getCartQuery(string $maskedQuoteId)
     }
   }
 }
+QUERY;
+    }
+
+    /**
+     * @magentoConfigFixture default_store sales/gift_options/allow_items 1
+     * @magentoApiDataFixture Magento/GiftMessage/_files/guest/quote_with_item_message.php
+     * @throws Exception
+     */
+    public function testUpdateGiftMessageCartForItem()
+    {
+        $query = $this->getUpdateGiftMessageQuery();
+        foreach ($this->graphQlMutation($query)['updateCartItems']['cart']['items'] as $item) {
+            self::assertArrayHasKey('gift_message', $item);
+            self::assertSame('Alex', $item['gift_message']['to']);
+            self::assertSame('Mike', $item['gift_message']['from']);
+            self::assertSame('Best regards.', $item['gift_message']['message']);
+        }
+    }
+
+    /**
+     * @magentoConfigFixture default_store sales/gift_options/allow_items 0
+     * @magentoApiDataFixture Magento/GiftMessage/_files/guest/quote_with_item_message.php
+     * @throws Exception
+     */
+    public function testUpdateGiftMessageCartForItemNotAllow()
+    {
+        $query = $this->getUpdateGiftMessageQuery();
+        foreach ($this->graphQlMutation($query)['updateCartItems']['cart']['items'] as $item) {
+            self::assertNull($item['gift_message']);
+        }
+    }
+
+    private function getUpdateGiftMessageQuery()
+    {
+        $quote = $this->quoteFactory->create();
+        $this->quoteResource->load($quote, 'test_guest_order_with_gift_message', 'reserved_order_id');
+        $maskedQuoteId = $this->quoteIdToMaskedId->execute((int)$quote->getId());
+        $itemId = (int)$quote->getItemByProduct($this->productRepository->get('simple'))->getId();
+
+        return <<<QUERY
+mutation {
+  updateCartItems(
+    input: {
+      cart_id: "$maskedQuoteId",
+      cart_items: [
+        {
+         cart_item_id: $itemId
+          quantity: 3
+         gift_message: {
+            to: "Alex"
+            from: "Mike"
+            message: "Best regards."
+          }
+        }
+      ]
+    }
+  ) {
+    cart {
+      items {
+        id
+        product {
+         name
+        }
+        quantity
+          ... on SimpleCartItem {
+          gift_message {
+            to
+            from
+            message
+          }
+        }
+     }
+    }
+  }
+}
 QUERY;
     }
 }