private void completeInitiatedSends() throws IOException {
        for (NetworkSend send : initiatedSends) {
            completeSend(send);
        }
        this.initiatedSends.clear();
    }
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