private function validateFailed(RequestInterface $request, ResponseInterface $response)
 {
     $req = Utils::getDirective($request, 'stale-if-error');
     $res = Utils::getDirective($response, 'stale-if-error');
     if (!$req && !$res) {
         return false;
     }
     $responseAge = Utils::getResponseAge($response);
     $maxAge = Utils::getMaxAge($response);
     if ($req && $responseAge - $maxAge > $req || $responseAge - $maxAge > $res) {
         return false;
     }
     return true;
 }
 /**
  * Test that a response with no max-age information returns null.
  */
 public function testGetMaxAgeNull()
 {
     $messageFactory = new MessageFactory();
     $response = $messageFactory->createResponse(200);
     $this->assertSame(null, Utils::getMaxAge($response));
 }