Symfony\Component\HttpFoundation\Response::hasVary PHP Method

    public function hasVary()
    {
        return null !== $this->headers->get('Vary');
    }

 public function testHasVary()
 {
     $response = new Response();
     $this->assertFalse($response->hasVary());
     $response->setVary('User-Agent');
     $this->assertTrue($response->hasVary());
 }