From ce6dd8572efc5802b5b9d9f2257b2dce30e8ff9d Mon Sep 17 00:00:00 2001
From: Pavel <psidorenko@comwrap.com>
Date: Thu, 15 Feb 2018 16:00:46 +0200
Subject: [PATCH 1/4] Issue-13556 Modified source model
 "app/code/Magento/CatalogInventory/Model/Source/Stock.php" - overridden
 parent method "addValueSortToCollection" for adding sorting by stock items
 qty.

---
 .../CatalogInventory/Model/Source/Stock.php   | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/app/code/Magento/CatalogInventory/Model/Source/Stock.php b/app/code/Magento/CatalogInventory/Model/Source/Stock.php
index f64026cce23a5..40283a26f4055 100644
--- a/app/code/Magento/CatalogInventory/Model/Source/Stock.php
+++ b/app/code/Magento/CatalogInventory/Model/Source/Stock.php
@@ -26,4 +26,23 @@ public function getAllOptions()
             ['value' => \Magento\CatalogInventory\Model\Stock::STOCK_OUT_OF_STOCK, 'label' => __('Out of Stock')]
         ];
     }
+
+    /**
+     * Add Value Sort To Collection Select
+     *
+     * @param \Magento\Eav\Model\Entity\Collection\AbstractCollection $collection
+     * @param string $dir
+     *
+     * @return $this
+     */
+    public function addValueSortToCollection($collection, $dir = \Magento\Framework\Data\Collection::SORT_ORDER_DESC)
+    {
+        $collection->getSelect()->joinLeft(
+            ['stock_item_table' => 'cataloginventory_stock_item'],
+            "e.entity_id=stock_item_table.product_id",
+            []
+        );
+        $collection->getSelect()->order("stock_item_table.qty $dir");
+        return $this
+    }
 }

From a6dc79ac003855cda3df4f17d4645f0dd29373dd Mon Sep 17 00:00:00 2001
From: Pavel <psidorenko@comwrap.com>
Date: Fri, 16 Feb 2018 12:48:09 +0200
Subject: [PATCH 2/4] Issue-13556 Syntax fixes in method
 Magento\CatalogInventory\Model\Source\Stock::addValueSortToCollection

---
 app/code/Magento/CatalogInventory/Model/Source/Stock.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/app/code/Magento/CatalogInventory/Model/Source/Stock.php b/app/code/Magento/CatalogInventory/Model/Source/Stock.php
index 40283a26f4055..d6b34ff15fb30 100644
--- a/app/code/Magento/CatalogInventory/Model/Source/Stock.php
+++ b/app/code/Magento/CatalogInventory/Model/Source/Stock.php
@@ -43,6 +43,6 @@ public function addValueSortToCollection($collection, $dir = \Magento\Framework\
             []
         );
         $collection->getSelect()->order("stock_item_table.qty $dir");
-        return $this
+        return $this;
     }
 }

From bcb553c40e0becae8a164f3902cd61c5e2d3447e Mon Sep 17 00:00:00 2001
From: Pavel <psidorenko@comwrap.com>
Date: Mon, 19 Feb 2018 11:58:58 +0200
Subject: [PATCH 3/4] Issue-13556 Edited comment in method
 Magento\CatalogInventory\Model\Source\Stock::addValueSortToCollection.

---
 app/code/Magento/CatalogInventory/Model/Source/Stock.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/app/code/Magento/CatalogInventory/Model/Source/Stock.php b/app/code/Magento/CatalogInventory/Model/Source/Stock.php
index d6b34ff15fb30..9ed891d1dcc0f 100644
--- a/app/code/Magento/CatalogInventory/Model/Source/Stock.php
+++ b/app/code/Magento/CatalogInventory/Model/Source/Stock.php
@@ -28,7 +28,7 @@ public function getAllOptions()
     }
 
     /**
-     * Add Value Sort To Collection Select
+     * Add Value Sort To Collection Select.
      *
      * @param \Magento\Eav\Model\Entity\Collection\AbstractCollection $collection
      * @param string $dir

From 551fa251b53b92743eb4fd830e2d029c30788449 Mon Sep 17 00:00:00 2001
From: Stanislav Idolov <sidolov@magento.com>
Date: Wed, 7 Mar 2018 16:29:00 +0200
Subject: [PATCH 4/4] magento/magento2#13691

---
 .../Test/Unit/Model/Source/StockTest.php      | 44 +++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 app/code/Magento/CatalogInventory/Test/Unit/Model/Source/StockTest.php

diff --git a/app/code/Magento/CatalogInventory/Test/Unit/Model/Source/StockTest.php b/app/code/Magento/CatalogInventory/Test/Unit/Model/Source/StockTest.php
new file mode 100644
index 0000000000000..11f41fcaf6d01
--- /dev/null
+++ b/app/code/Magento/CatalogInventory/Test/Unit/Model/Source/StockTest.php
@@ -0,0 +1,44 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+namespace Magento\CatalogInventory\Test\Unit\Model\Source;
+
+use PHPUnit\Framework\TestCase;
+
+class StockTest extends TestCase
+{
+    /**
+     * @var \Magento\CatalogInventory\Model\Source\Stock
+     */
+    private $model;
+
+    protected function setUp()
+    {
+        $this->model = new \Magento\CatalogInventory\Model\Source\Stock();
+    }
+
+    public function testAddValueSortToCollection()
+    {
+        $selectMock = $this->createMock(\Magento\Framework\DB\Select::class);
+        $collectionMock = $this->createMock(\Magento\Eav\Model\Entity\Collection\AbstractCollection::class);
+        $collectionMock->expects($this->atLeastOnce())->method('getSelect')->willReturn($selectMock);
+
+        $selectMock->expects($this->once())
+            ->method('joinLeft')
+            ->with(
+                ['stock_item_table' => 'cataloginventory_stock_item'],
+                "e.entity_id=stock_item_table.product_id",
+                []
+            )
+            ->willReturnSelf();
+        $selectMock->expects($this->once())
+            ->method('order')
+            ->with("stock_item_table.qty DESC")
+            ->willReturnSelf();
+
+        $this->model->addValueSortToCollection($collectionMock);
+    }
+}