private void completeSend(NetworkSend send) throws IOException {
        // Consume the send so that we will be able to send more requests to the destination
        try (ByteBufferChannel discardChannel = new ByteBufferChannel(send.size())) {
            while (!send.completed()) {
                send.writeTo(discardChannel);
            }
            completedSends.add(send);
            completedSendBuffers.add(discardChannel);
        }
    }
Simulate a server disconnect. This id will be present in {@link #disconnected()} on
the next {@link #poll(long)}.
clients/src/test/java/org/apache/kafka/test/MockSelector.java