private void respondToProduce(TopicPartition tp, Errors error, long offset) {
        client.respond(
            request -> request instanceof ProduceRequest,
            produceResponse(tp, offset, error, 0)
        );

    }
Tests the code path where the target node to send FindCoordinator or InitProducerId
is not ready.
clients/src/test/java/org/apache/kafka/clients/producer/internals/SenderTest.java