public function testServerIsImmutableOnceDeviceRetrieved()
 {
     $config = $this->config;
     $userAgent = new Zend_Http_UserAgent($config);
     $device = $userAgent->getDevice();
     $this->setExpectedException('Zend_Http_UserAgent_Exception', 'immutable');
     $userAgent->setServerValue('HTTP_ACCEPT', 'application/json');
 }