@Override
  public List<String> connected() {
    if (state == MockSelectorState.IdlePoll) {
      return new ArrayList<>();
    }
    return connected;
  }
Returns a list of connection ids created between the last two poll() calls (or since instantiation if only one
{@link #poll(long, List)} was done).
@return a list of connection ids.
ambry-network/src/test/java/com/github/ambry/network/SocketNetworkClientTest.java