ImageLoadingAttributeTest.php

<?php

declare (strict_types=1);
namespace Drupal\Tests\system\Functional\Theme;

use Drupal\Tests\BrowserTestBase;

/**
 * Tests lazy loading for images.
 *
 * @group Theme
 */
class ImageLoadingAttributeTest extends BrowserTestBase {
  
  /**
   * {@inheritdoc}
   */
  protected static $modules = [
    'image_lazy_load_test',
  ];
  
  /**
   * {@inheritdoc}
   */
  protected $defaultTheme = 'stark';
  
  /**
   * Tests that loading attribute is enabled for images.
   */
  public function testImageLoadingAttribute() : void {
    $assert = $this->assertSession();
    // Get page under test.
    $this->drupalGet('image-lazy-load-test');
    // Loading attribute is added when image dimensions has been set.
    $assert->elementAttributeExists('css', '#with-dimensions img', 'loading');
    $assert->elementAttributeContains('css', '#with-dimensions img', 'loading', 'lazy');
    // Loading attribute with lazy default value can be overridden.
    $assert->elementAttributeContains('css', '#override-loading-attribute img', 'loading', 'eager');
    // Without image dimensions loading attribute is not generated.
    $element = $assert->elementExists('css', '#without-dimensions img');
    $this->assertFalse($element->hasAttribute('loading'));
  }

}