Cover changes with unit test

app/code/Magento/Theme/Test/Unit/Block/Html/PagerTest.php

@@ -0,0 +1,109 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\Theme\Test\Unit\Block\Html;
+
+use Magento\Framework\App\Config;
+use Magento\Framework\Data\Collection;
+use Magento\Framework\TestFramework\Unit\Helper\ObjectManager;
+use Magento\Framework\UrlInterface;
+use Magento\Framework\View\Element\Template\Context;
+use Magento\Theme\Block\Html\Pager;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Test For Page class
+ */
+class PagerTest extends TestCase
+{
+
+    /**
+     * @var Pager $pager
+     */
+    private $pager;
+
+    /**
+     * @var Context $context
+     */
+    private $context;
+
+    /**
+     * @var Config $scopeConfig
+     */
+    private $scopeConfig;
+
+    /**
+     * @var ObjectManager $objectManager
+     */
+    private $objectManager;
+
+    /**
+     * @var UrlInterface $urlBuilderMock
+     */
+    private $urlBuilderMock;
+
+    /**
+     * @inheritdoc
+     */
+    protected function setUp()
+    {
+        $this->context = $this->createMock(Context::class);
+        $this->urlBuilderMock = $this->createMock(UrlInterface::class);
+        $this->context->expects($this->any())
+            ->method('getUrlBuilder')
+            ->willReturn($this->urlBuilderMock);
+        $this->scopeConfig = $this->createMock(Config::class);
+        $this->pager = (new ObjectManager($this))->getObject(
+            Pager::class,
+            ['context' => $this->context]
+        );
+    }
+
+    /**
+     * Verify current page Url
+     *
+     * @return void
+     */
+    public function testGetPageUrl(): void
+    {
+        $expectedPageUrl = 'page-url';
+        $this->urlBuilderMock->expects($this->once())
+            ->method('getUrl')
+            ->willReturn($expectedPageUrl);
+        $this->assertEquals($expectedPageUrl, $this->pager->getPageUrl(0));
+    }
+
+    /**
+     * Verify get pages method.
+     *
+     * @return void
+     */
+    public function testGetPages(): void
+    {
+        $expectedPages = range(1, 5);
+        $collectionMock = $this->createMock(Collection::class);
+        $collectionMock->expects($this->exactly(2))
+                       ->method('getCurPage')
+                       ->willReturn(2);
+        $collectionMock->expects($this->any())
+            ->method('getLastPageNumber')
+            ->willReturn(10);
+        $this->setCollectionProperty($collectionMock);
+        $this->assertEquals($expectedPages, $this->pager->getPages());
+    }
+
+    /**
+     * Set Collection
+     *
+     * @return void
+     */
+    private function setCollectionProperty($collection): void
+    {
+        $reflection = new \ReflectionClass($this->pager);
+        $reflection_property = $reflection->getProperty('_collection');
+        $reflection_property->setAccessible(true);
+        $reflection_property->setValue($this->pager, $collection);
+    }
+}