@Test
    public void testDescribeProducers() throws Exception {
        try (AdminClientUnitTestEnv env = mockClientEnv()) {
            TopicPartition topicPartition = new TopicPartition("foo", 0);

            Node leader = env.cluster().nodes().iterator().next();
            expectMetadataRequest(env, topicPartition, leader);

            List<ProducerState> expected = asList(
                new ProducerState(12345L, 15, 30, env.time().milliseconds(),
                    OptionalInt.of(99), OptionalLong.empty()),
                new ProducerState(12345L, 15, 30, env.time().milliseconds(),
                    OptionalInt.empty(), OptionalLong.of(23423L))
            );

            DescribeProducersResponse response = buildDescribeProducersResponse(
                topicPartition,
                expected
            );

            env.kafkaClient().prepareResponseFrom(
                request -> request instanceof DescribeProducersRequest,
                response,
                leader
            );

            DescribeProducersResult result = env.adminClient().describeProducers(singleton(topicPartition));
            KafkaFuture<DescribeProducersResult.PartitionProducerState> partitionFuture =
                result.partitionResult(topicPartition);
            assertEquals(new HashSet<>(expected), new HashSet<>(partitionFuture.get().activeProducers()));
        }
    }
Test that we propagate exceptions encountered when fetching metadata.
clients/src/test/java/org/apache/kafka/clients/admin/KafkaAdminClientTest.java