public function testSendHeaders() {
$response = new Response();
$headers = $response
->sendHeaders();
$this
->assertObjectHasAttribute('headers', $headers);
$this
->assertObjectHasAttribute('content', $headers);
$this
->assertObjectHasAttribute('version', $headers);
$this
->assertObjectHasAttribute('statusCode', $headers);
$this
->assertObjectHasAttribute('statusText', $headers);
$this
->assertObjectHasAttribute('charset', $headers);
}