public function theResponseShouldExpireInTheFuture()
{
$date = new \DateTime($this->request->getHttpHeader('Date'));
$expires = new \DateTime($this->request->getHttpHeader('Expires'));
$this->assertSame(1, $expires->diff($date)->invert, sprintf('The response doesn\'t expire in the future (%s)', $expires->format(DATE_ATOM)));
}