public function testSetExpires() {
$response = new Response();
$response
->setExpires(null);
$this
->assertNull($response
->getExpires(), '->setExpires() remove the header when passed null');
$now = new \DateTime();
$response
->setExpires($now);
$this
->assertEquals($response
->getExpires()
->getTimestamp(), $now
->getTimestamp());
}