@Override
  public List<NetworkSend> completedSends() {
    if (state == MockSelectorState.IdlePoll) {
      return new ArrayList<>();
    }
    List<NetworkSend> toReturn = sends;
    sends = new ArrayList<>();
    return toReturn;
  }
Returns a list of {@link NetworkSend} sent as part of the last poll.
@return a lit of {@link NetworkSend} initiated previously.
ambry-network/src/test/java/com/github/ambry/network/SocketNetworkClientTest.java