improved solution and test coverage

Author: Usik2203

app/code/Magento/CatalogCustomerGraphQl/Model/Resolver/PriceTiers.php

@@ -155,7 +155,8 @@ private function formatAndFilterTierPrices(
         array $tierPrices,
         string $currencyCode
     ): array {
-        $this->resetFormatAndFilterTierPrices();
+        $this->formatAndFilterTierPrices = [];
+        $this->tierPricesQty = [];
         foreach ($tierPrices as $key => $tierPrice) {
             $tierPrice->setValue($this->priceCurrency->convertAndRound($tierPrice->getValue()));
             $this->formatTierPrices($productPrice, $currencyCode, $tierPrice);
@@ -215,14 +216,4 @@ private function filterTierPrices(
             $this->tierPricesQty[$qty] = $key;
         }
     }
-
-    /**
-     *  Remove all element from formatAndFilterTierPrices
-     */
-    private function resetFormatAndFilterTierPrices()
-    {
-        foreach ($this->formatAndFilterTierPrices as $key => $value) {
-            unset($this->formatAndFilterTierPrices[$key]);
-        }
-    }
 }

dev/tests/api-functional/testsuite/Magento/GraphQl/CatalogCustomer/PriceTiersTest.php

@@ -118,6 +118,7 @@ public function testGetLowestPriceForGuest()
     }
 
     /**
+     * @magentoApiDataFixture Magento/Catalog/_files/simple_product_without_tier_price.php
      * @magentoApiDataFixture Magento/Catalog/_files/three_simple_products_with_tier_price.php
      */
     public function testGetCorrectDisplaingTierPriceForProducts()
@@ -140,9 +141,10 @@ public function testGetCorrectDisplaingTierPriceForProducts()
 }
 QUERY;
         $response = $this->graphQlQuery($query);
-        $this->assertCount(1, $response['products']['items'][0]['price_tiers']);
+        $this->assertCount(0, $response['products']['items'][0]['price_tiers']);
         $this->assertCount(1, $response['products']['items'][1]['price_tiers']);
         $this->assertCount(1, $response['products']['items'][2]['price_tiers']);
+        $this->assertCount(1, $response['products']['items'][3]['price_tiers']);
     }
 
     /**

dev/tests/integration/testsuite/Magento/Catalog/_files/simple_product_without_tier_price.php

@@ -0,0 +1,44 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+use Magento\Catalog\Api\ProductRepositoryInterface;
+use Magento\Catalog\Model\Product;
+use Magento\Catalog\Model\Product\Attribute\Source\Status;
+use Magento\Catalog\Model\Product\Type;
+use Magento\Catalog\Model\Product\Visibility;
+use Magento\Store\Api\Data\WebsiteInterface;
+use Magento\Store\Api\WebsiteRepositoryInterface;
+use Magento\TestFramework\Helper\Bootstrap;
+
+$objectManager = Bootstrap::getObjectManager();
+
+/** @var WebsiteInterface $adminWebsite */
+$adminWebsite = $objectManager->get(WebsiteRepositoryInterface::class)->get('admin');
+
+/** @var ProductRepositoryInterface $productRepository */
+$productRepository = $objectManager->get(ProductRepositoryInterface::class);
+/** @var $product Product */
+$product = $objectManager->create(Product::class);
+$product->setTypeId(Type::TYPE_SIMPLE)
+->setAttributeSetId($product->getDefaultAttributeSetId())
+->setWebsiteIds([1])
+->setName('Simple Product ' . 10)
+->setSku('simple_10')
+->setPrice(22)
+->setWeight(1)
+->setVisibility(Visibility::VISIBILITY_BOTH)
+->setStatus(Status::STATUS_ENABLED)
+->setStockData(
+    [
+        'use_config_manage_stock' => 1,
+        'qty' => 100,
+        'is_qty_decimal' => 0,
+        'is_in_stock' => 1,
+    ]
+);
+
+$productRepository->save($product);

dev/tests/integration/testsuite/Magento/Catalog/_files/simple_product_without_tier_price_rollback.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+use Magento\Catalog\Api\ProductRepositoryInterface;
+use Magento\Framework\Exception\NoSuchEntityException;
+use Magento\Framework\Registry;
+use Magento\TestFramework\Helper\Bootstrap;
+
+Bootstrap::getInstance()->getInstance()->reinitialize();
+
+/** @var Registry $registry */
+$registry = Bootstrap::getObjectManager()->get(Registry::class);
+
+$registry->unregister('isSecureArea');
+$registry->register('isSecureArea', true);
+
+/** @var ProductRepositoryInterface $productRepository */
+$productRepository = Bootstrap::getObjectManager()->get(ProductRepositoryInterface::class);
+try {
+    $product = $productRepository->get('simple_10', false, null, true);
+    $productRepository->delete($product);
+} catch (NoSuchEntityException $e) {
+}
+$registry->unregister('isSecureArea');
+$registry->register('isSecureArea', false);