@Override
  public List<NetworkReceive> completedReceives() {
    List<NetworkReceive> toReturn = receives;
    receives = new ArrayList<NetworkReceive>();
    return toReturn;
  }
Returns a list of {@link NetworkReceive} constructed in the last poll.
@return a list of {@link NetworkReceive} for every initiated send.
ambry-router/src/test/java/com/github/ambry/router/MockSelector.java