@Test
    public void testRetryDescribeTransactionsAfterNotCoordinatorError() throws Exception {
        MockTime time = new MockTime();
        int retryBackoffMs = 100;
        Cluster cluster = mockCluster(3, 0);
        Map<String, Object> configOverride = newStrMap(AdminClientConfig.RETRY_BACKOFF_MS_CONFIG, "" + retryBackoffMs);

        try (AdminClientUnitTestEnv env = new AdminClientUnitTestEnv(time, cluster, configOverride)) {
            String transactionalId = "foo";

            Iterator<Node> nodeIterator = env.cluster().nodes().iterator();
            Node coordinator1 = nodeIterator.next();
            Node coordinator2 = nodeIterator.next();

            env.kafkaClient().prepareResponse(
                request -> request instanceof FindCoordinatorRequest,
                new FindCoordinatorResponse(new FindCoordinatorResponseData()
                        .setCoordinators(singletonList(new FindCoordinatorResponseData.Coordinator()
                                .setKey(transactionalId)
                                .setErrorCode(Errors.NONE.code())
                                .setNodeId(coordinator1.id())
                                .setHost(coordinator1.host())
                                .setPort(coordinator1.port()))))
            );

            env.kafkaClient().prepareResponseFrom(
                request -> {
                    if (!(request instanceof DescribeTransactionsRequest)) {
                        return false;
                    } else {
                        // Backoff needed here for the retry of FindCoordinator
                        time.sleep(retryBackoffMs);
                        return true;
                    }
                },
                new DescribeTransactionsResponse(new DescribeTransactionsResponseData().setTransactionStates(
                    singletonList(new DescribeTransactionsResponseData.TransactionState()
                        .setErrorCode(Errors.NOT_COORDINATOR.code())
                        .setTransactionalId(transactionalId)
                    )
                )),
                coordinator1
            );

            env.kafkaClient().prepareResponse(
                request -> request instanceof FindCoordinatorRequest,
                new FindCoordinatorResponse(new FindCoordinatorResponseData()
                        .setCoordinators(singletonList(new FindCoordinatorResponseData.Coordinator()
                                .setKey(transactionalId)
                                .setErrorCode(Errors.NONE.code())
                                .setNodeId(coordinator2.id())
                                .setHost(coordinator2.host())
                                .setPort(coordinator2.port()))))
            );

            TransactionDescription expected = new TransactionDescription(
                coordinator2.id(), TransactionState.COMPLETE_COMMIT, 12345L,
                15, 10000L, OptionalLong.empty(), emptySet());

            env.kafkaClient().prepareResponseFrom(
                request -> request instanceof DescribeTransactionsRequest,
                new DescribeTransactionsResponse(new DescribeTransactionsResponseData().setTransactionStates(
                    singletonList(new DescribeTransactionsResponseData.TransactionState()
                        .setErrorCode(Errors.NONE.code())
                        .setProducerEpoch((short) expected.producerEpoch())
                        .setProducerId(expected.producerId())
                        .setTransactionalId(transactionalId)
                        .setTransactionTimeoutMs(10000)
                        .setTransactionStartTimeMs(-1)
                        .setTransactionState(expected.state().toString())
                    )
                )),
                coordinator2
            );

            DescribeTransactionsResult result = env.adminClient().describeTransactions(singleton(transactionalId));
            KafkaFuture<TransactionDescription> future = result.description(transactionalId);
            assertEquals(expected, future.get());
        }
    }
Test that we propagate exceptions encountered when fetching metadata.
clients/src/test/java/org/apache/kafka/clients/admin/KafkaAdminClientTest.java