FolderTest.php

<?php

namespace Drupal\FunctionalTests;

use Drupal\Tests\BrowserTestBase;

/**
 * This test will check BrowserTestBase's treatment of hook_install during
 * setUp.
 * Image module is used for test.
 *
 * @group browsertestbase
 */
class FolderTest extends BrowserTestBase {
    
    /**
     * Modules to enable.
     *
     * @var array
     */
    public static $modules = [
        'image',
    ];
    
    /**
     * {@inheritdoc}
     */
    protected $defaultTheme = 'stark';
    public function testFolderSetup() {
        $directory = 'public://styles';
        $this->assertTrue(\Drupal::service('file_system')->prepareDirectory($directory, FALSE), 'Directory created.');
    }

}