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'));
    }

}