MC-17524: Child product is not addable to Cart from PLP if it does not have default source assigned

Author: Mastiuhin Olexandr

app/code/Magento/GroupedCatalogInventory/Plugin/OutOfStockFilter.php

@@ -50,9 +50,8 @@ public function afterPrepareForCartAdvanced(Grouped $subject, $result, DataObjec
         // Only remove out-of-stock products if no quantities were specified
         if (is_array($result) && !empty($result) && !$buyRequest->getData('super_group')) {
             foreach ($result as $index => $cartItem) {
-                $prodId = $cartItem->getId();
-                $productStockStatus = $this->stockRegistry->getProductStockStatus($prodId);
-                if ($productStockStatus == StockStatusInterface::STATUS_OUT_OF_STOCK) {
+                $productStockStatus = $this->stockRegistry->getProductStockStatus($cartItem->getId());
+                if ($productStockStatus === StockStatusInterface::STATUS_OUT_OF_STOCK) {
                     unset($result[$index]);
                 }
             }

app/code/Magento/GroupedCatalogInventory/Test/Unit/Plugin/OutOfStockFilterTest.php

@@ -16,7 +16,6 @@
 use Magento\GroupedProduct\Model\Product\Type\Grouped;
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
-
 use Magento\CatalogInventory\Api\StockRegistryInterface;
 
 /**