[Newsletter] Refactor code and Cover Model/Observer class by Unit Test

app/code/Magento/Newsletter/Model/Observer.php

@@ -3,29 +3,50 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+
+declare(strict_types=1);
+
 namespace Magento\Newsletter\Model;
 
+use Magento\Newsletter\Model\ResourceModel\Queue\Collection;
+use Magento\Newsletter\Model\ResourceModel\Queue\CollectionFactory;
+
 /**
  * Newsletter module observer
  *
  * @SuppressWarnings(PHPMD.LongVariable)
  */
 class Observer
 {
+    /**
+     * Number of queue
+     */
+    private const COUNT_OF_QUEUE = 3;
+
+    /**
+     * Number of subscriptions
+     */
+    private const COUNT_OF_SUBSCRIPTIONS = 20;
+
+    /**
+     * First page in collection
+     */
+    private const FIRST_PAGE = 1;
+
     /**
      * Queue collection factory
      *
-     * @var \Magento\Newsletter\Model\ResourceModel\Queue\CollectionFactory
+     * @var CollectionFactory
      */
     protected $_queueCollectionFactory;
 
     /**
      * Construct
      *
-     * @param \Magento\Newsletter\Model\ResourceModel\Queue\CollectionFactory $queueCollectionFactory
+     * @param CollectionFactory $queueCollectionFactory
      */
     public function __construct(
-        \Magento\Newsletter\Model\ResourceModel\Queue\CollectionFactory $queueCollectionFactory
+        CollectionFactory $queueCollectionFactory
     ) {
         $this->_queueCollectionFactory = $queueCollectionFactory;
     }
@@ -37,13 +58,11 @@ public function __construct(
      */
     public function scheduledSend()
     {
-        $countOfQueue  = 3;
-        $countOfSubscriptions = 20;
-
-        /** @var \Magento\Newsletter\Model\ResourceModel\Queue\Collection $collection */
+        /** @var Collection $collection */
         $collection = $this->_queueCollectionFactory->create();
-        $collection->setPageSize($countOfQueue)->setCurPage(1)->addOnlyForSendingFilter()->load();
+        $collection->setPageSize(self::COUNT_OF_QUEUE)
+            ->setCurPage(self::FIRST_PAGE)->addOnlyForSendingFilter()->load();
 
-        $collection->walk('sendPerSubscriber', [$countOfSubscriptions]);
+        $collection->walk('sendPerSubscriber', [self::COUNT_OF_SUBSCRIPTIONS]);
     }
 }

app/code/Magento/Newsletter/Test/Unit/Model/ObserverTest.php

@@ -0,0 +1,63 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Newsletter\Test\Unit\Model;
+
+use Magento\Framework\TestFramework\Unit\Helper\ObjectManager as ObjectManagerHelper;
+use Magento\Newsletter\Model\Observer;
+use Magento\Newsletter\Model\ResourceModel\Queue\Collection;
+use Magento\Newsletter\Model\ResourceModel\Queue\CollectionFactory;
+use PHPUnit\Framework\TestCase;
+
+class ObserverTest extends TestCase
+{
+    /**
+     * @var Observer
+     */
+    private $model;
+
+    /**
+     * @var CollectionFactory|\PHPUnit_Framework_MockObject_MockObject
+     */
+    private $collectionFactoryMock;
+
+    /**
+     * Setup environment for test
+     */
+    protected function setUp()
+    {
+        $objectManager = new ObjectManagerHelper($this);
+
+        $this->collectionFactoryMock = $this->createPartialMock(
+            CollectionFactory::class,
+            ['create']
+        );
+
+        $this->model = $objectManager->getObject(
+            Observer::class,
+            [
+                'queueCollectionFactory' => $this->collectionFactoryMock
+            ]
+        );
+    }
+
+    /**
+     * Test scheduledSend() method
+     */
+    public function testScheduledSend()
+    {
+        $collectionMock = $this->createMock(Collection::class);
+        $this->collectionFactoryMock->expects($this->once())->method('create')->willReturn($collectionMock);
+        $collectionMock->expects($this->once())->method('setPageSize')->with(3)->willReturnSelf();
+        $collectionMock->expects($this->once())->method('setCurPage')->with(1)->willReturnSelf();
+        $collectionMock->expects($this->once())->method('addOnlyForSendingFilter')->willReturnSelf();
+        $collectionMock->expects($this->once())->method('load')->willReturnSelf();
+        $collectionMock->expects($this->once())->method('walk')->with('sendPerSubscriber', [20]);
+
+        $this->model->scheduledSend();
+    }
+}