MAGETWO-75458: [Backport] - Fix overwrite default value image/file with NULL #10253 - for 2.2

Author: VladimirZaets

dev/tests/integration/testsuite/Magento/Config/Model/Config/Backend/FileTest.php

@@ -0,0 +1,57 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\Config\Model\Config\Backend;
+
+use Magento\TestFramework\Helper\Bootstrap;
+
+class FileTest extends \PHPUnit\Framework\TestCase
+{
+    /**
+     * @var \Magento\Config\Model\Config\Backend\File
+     */
+    private $_model = null;
+
+    protected function setUp()
+    {
+        parent::setUp();
+        $this->_model = \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(
+            \Magento\Config\Model\Config\Backend\File::class
+        );
+    }
+
+    /**
+     * @magentoDbIsolation disabled
+     * @magentoAppArea adminhtml
+     */
+    public function testFileSave()
+    {
+        $groups = [
+            'identity' => [
+                'fields' => [
+                    'logo' => [
+                        'value' => [
+                            'value' => 'example.png'
+                        ],
+                    ],
+                ],
+            ],
+        ];
+        $expected = [
+            'sales/identity/logo' => 'example.png'
+        ];
+        $section = 'sales';
+        $objectManager = Bootstrap::getObjectManager();
+
+        /** @var $_configDataObject \Magento\Config\Model\Config */
+        $_configDataObject = $objectManager->create(\Magento\Config\Model\Config::class);
+        $_configDataObject->setSection($section)->setWebsite('base')->setGroups($groups)->save();
+
+        $_configDataObject = $objectManager->create(\Magento\Config\Model\Config::class);
+        $_configData = $_configDataObject->setSection('sales/identity')->setWebsite('base')->load();
+
+        $this->assertEquals($expected, $_configData);
+    }
+}