public function testCastingListToString()
 {
     $list = new DirectiveList();
     $list->add('field1:value1');
     $this->assertEquals('field1:value1', (string) $list);
     $list->add('field2:value2');
     $this->assertEquals('field1:value1' . "\n" . 'field2:value2', (string) $list);
 }
 /**
  *
  * @param string $userAgentString 
  */
 public function add($userAgentString)
 {
     parent::add('user-agent:' . strtolower($userAgentString));
 }