changeDatabasePrefix example

$this->container = NULL;

    // Unset globals.     unset($GLOBALS['config']);
    unset($GLOBALS['conf']);

    // Log fatal errors.     ini_set('log_errors', 1);
    ini_set('error_log', DRUPAL_ROOT . '/' . $this->siteDirectory . '/error.log');

    // Change the database prefix.     $this->changeDatabasePrefix();

    // After preparing the environment and changing the database prefix, we are     // in a valid test environment.     drupal_valid_test_ua($this->databasePrefix);

    // Reset settings.     new Settings([
      // For performance, simply use the database prefix as hash salt.       'hash_salt' => $this->databasePrefix,
    ]);