    def test_confirmation_obj_not_exist_error(self) -> None:
        """Since the key is a param input by the user to the registration endpoint,
        if it inserts an invalid value, the confirmation object won't be found. This
        tests if, in that scenario, we handle the exception by redirecting the user to
        the confirmation_link_expired_error page.
        """
        email = self.nonreg_email("alice")
        password = "password"
        realm = get_realm("zulip")
        inviter = self.example_user("iago")
        prereg_user = PreregistrationUser.objects.create(
            email=email, referred_by=inviter, realm=realm
        )
        confirmation_link = create_confirmation_link(prereg_user, Confirmation.USER_REGISTRATION)

        registration_key = "invalid_confirmation_key"
        url = "/accounts/register/"
        response = self.client_post(
            url, {"key": registration_key, "from_confirmation": 1, "full_nme": "alice"}
        )
        self.assertEqual(response.status_code, 404)
        self.assert_in_response("The registration link has expired or is not valid.", response)

        registration_key = confirmation_link.split("/")[-1]
        response = self.client_post(
            url, {"key": registration_key, "from_confirmation": 1, "full_nme": "alice"}
        )
        self.assert_in_success_response(["We just need you to do one last thing."], response)
        response = self.submit_reg_form_for_user(email, password, key=registration_key)
        self.assertEqual(response.status_code, 302)
According to WASC, "Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization."