public function assertResponseIs($group) {
        $this->requireResponse();
        $range = $this->getResponseCodeGroupRange($group);

        try {
            Assertion::range($code = $this->response->getStatusCode(), $range['min'], $range['max']);
        } catch (AssertionFailure $e) {
            throw new AssertionFailedException(sprintf(
                'Expected response group "%s", got "%s" (response code: %d).',
                $group,
                $this->getResponseGroup($code),
                $code
            ));
        }
    }