public function assertResponseCodeIsNot($code) {
        $this->requireResponse();

        try {
            Assertion::notSame(
                $actual = $this->response->getStatusCode(),
                $this->validateResponseCode($code),
                sprintf('Did not expect response code %d.', $actual)
            );
        } catch (AssertionFailure $e) {
            throw new AssertionFailedException($e->getMessage());
        }
    }