FolderTest.php

<?php

/**
 * @file
 * Definition of Drupal\simpletest\Tests\FolderTest.
 */
namespace Drupal\simpletest\Tests;

use Drupal\simpletest\WebTestBase;

/**
 * Test Folder creation
 */
class FolderTest extends WebTestBase {

  /**
   * Modules to enable.
   *
   * @var array
   */
  public static $modules = array(
    'image',
  );
  public static function getInfo() {
    return array(
      'name' => 'Testing SimpleTest setUp',
      'description' => "This test will check SimpleTest's treatment of hook_install during setUp.  Image module is used for test.",
      'group' => 'SimpleTest',
    );
  }
  function testFolderSetup() {
    $directory = file_default_scheme() . '://styles';
    $this
      ->assertTrue(file_prepare_directory($directory, FALSE), "Directory created.");
  }

}