            let ps = PoolService::new();
            assert_match!(Err(PoolError::InvalidHandle(_)), ps.send_tx(-1, "txn"));
        }

        #[test]
        fn pool_close_works_for_invalid_handle() {
            TestUtils::cleanup_storage();
            let ps = PoolService::new();
            assert_match!(Err(PoolError::InvalidHandle(_)), ps.close(-1));
        }