Contao\Environment::set PHP Method

    public static function set($strKey, $varValue)
    {
        static::$arrCache[$strKey] = $varValue;
    }

 /**
  * {@inheritdoc}
  */
 public static function setupBeforeClass()
 {
     Environment::reset();
     Environment::set('path', '/core');
     require __DIR__ . '/../../src/Resources/contao/config/default.php';
     require __DIR__ . '/../../src/Resources/contao/config/agents.php';
 }