@Override
    public int inFlightRequestCount(String node) {
        int result = 0;
        for (ClientRequest req : requests) {
            if (req.destination().equals(node))
                ++result;
        }
        return result;
    }
Raise an unsupported version error on the next request if it matches the given matcher.
If the matcher does not match, {@link KafkaClient#send(ClientRequest, long)} will throw IllegalStateException.
@param matcher The request matcher to apply
clients/src/test/java/org/apache/kafka/clients/MockClient.java