/**
  * Add tracks from a passed in 'OrderEvents\ITrackingNumberIterable' instance to a passed in
  * 'sales/order_shipment' instance.
  * @param  OrderEvents\ITrackingNumberIterable $trackingNumbers
  * @param  Mage_Sales_Model_Order_Shipment $shipment
  * @return self
  */
 protected function _addAllTrackings(OrderEvents\ITrackingNumberIterable $trackingNumbers, Mage_Sales_Model_Order_Shipment $shipment)
 {
     foreach ($trackingNumbers as $track) {
         $shipment->addTrack($this->_initNewTrackInstance($track));
     }
     return $this;
 }