isImmutable example

$response = new Response();
        $response->setImmutable();

        $this->assertTrue($response->headers->hasCacheControlDirective('immutable'));
    }

    public function testIsImmutable()
    {
        $response = new Response();
        $response->setImmutable();

        $this->assertTrue($response->isImmutable());
    }

    public function testSetDate()
    {
        $response = new Response();
        $response->setDate(\DateTime::createFromFormat(\DateTimeInterface::ATOM, '2013-01-26T09:21:56+0100', new \DateTimeZone('Europe/Berlin')));

        $this->assertEquals('2013-01-26T08:21:56+00:00', $response->getDate()->format(\DateTimeInterface::ATOM));
    }

    public function testSetDateWithImmutable()
    {