public function setPayloadCalledTwice()
 {
     $fixture = new RestRequest();
     $fixture->setPayload(array('title' => 'New issue'), new RestXmlSerializer());
     $fixture->setPayload(array('title' => 'New issue'), new RestJsonSerializer());
     $this->assertEquals('application/json; charset=utf-8', $fixture->getHeader('Content-Type'));
 }