MC-39104: 2 error messages in Cart when product is out of stock

Author: rostyslav-hymon

app/code/Magento/CatalogInventory/Model/Quote/Item/QuantityValidator.php

@@ -165,6 +165,8 @@ public function validate(Observer $observer)
                         Data::ERROR_QTY,
                         __('This product is out of stock.')
                     );
+                } else {
+                    $quoteItem->addErrorInfo(null, Data::ERROR_QTY);
                 }
                 $quoteItem->getQuote()->addErrorInfo(
                     'stock',

app/code/Magento/ConfigurableProduct/Test/Mftf/Test/NoOptionAvailableToConfigureDisabledProductTest.xml

@@ -125,7 +125,7 @@
         <actionGroup ref="AdminSetStockStatusActionGroup" stepKey="outOfStockStatus">
             <argument name="stockStatus" value="Out of Stock"/>
         </actionGroup>
-      
+
         <actionGroup ref="SaveProductFormActionGroup" stepKey="saveSecondProductForm"/>
         <!-- Go to created customer page -->
         <comment userInput="Go to created customer page" stepKey="goToCreatedCustomerPage"/>
@@ -158,7 +158,7 @@
         <waitForPageLoad stepKey="waitForPageLoad"/>
         <click selector="{{AdminOrderFormItemsSection.addSelected}}" stepKey="clickToAddProductToOrder"/>
         <waitForPageLoad stepKey="waitForNewOrderPageLoad"/>
-        <see userInput="This product is out of stock." stepKey="seeTheErrorMessageDisplayed"/>
+        <see userInput="There are no source items with the in stock status" stepKey="seeTheErrorMessageDisplayed"/>
 
         <actionGroup ref="NavigateToNewOrderPageExistingCustomerActionGroup" stepKey="createNewOrderThirdTime">
             <argument name="customer" value="$createCustomer$"/>

dev/tests/api-functional/testsuite/Magento/Quote/Api/GuestCartItemRepositoryTest.php

@@ -265,7 +265,7 @@ public function updateItemDataProvider(): array
                     'use_config_backorders' => 0,
                     'backorders' => Stock::BACKORDERS_NO,
                 ],
-                'This product is out of stock.'
+                'There are no source items with the in stock status'
             ],
             [
                 [