public function assertResponseHeaderIsNot($header, $value) {
        $this->requireResponse();

        try {
            Assertion::notSame(
                $this->response->getHeaderLine($header),
                $value,
                sprintf(
                    'Did not expect the "%s" response header to be "%s".',
                    $header,
                    $value
                )
            );
        } catch (AssertionFailure $e) {
            throw new AssertionFailedException($e->getMessage());
        }
    }