void sendIdempotentProducerResponse(int expectedSequence, TopicPartition tp, Errors responseError, long responseOffset) {
        sendIdempotentProducerResponse(expectedSequence, tp, responseError, responseOffset, -1L);
    }
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