Magento – Mass Action not sending all data

I've created a mass action for my custom grid. i've encountered a weird problem which is when i check all the checkboxes, it won't send any post id data when i try to retrieve it with:

$this->getRequest->getParams();

but when i don't check all of them, it will send all the data that has been checked, here's my mass action code in xml:

<massaction name="listing_massaction">
  <action name="test">
    <argument name="data" xsi:type="array">
      <item name="config" xsi:type="array">
          <item name="type" xsi:type="string">test</item>
          <item name="label" xsi:type="string" translate="true">Test</item>
          <item name="url" xsi:type="url" path="namespace_module/test/massTest"/>
      </item>
    </argument>
  </action>
</massaction>

MassTest.php:

use Magento\Backend\App\Action\Context;
use Magento\Ui\Component\MassAction\Filter;
use Magento\Framework\Controller\ResultFactory;
use Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection;

class MassTest extends \Magento\Backend\App\Action
{

   public function __construct(
       Context $context,
       Filter $filter,
       \Namespace\Module\Model\ResourceModel\Test\CollectionFactory $collectionFactory
   ) {
       $this->filter = $filter;
       $this->_listingProduct = $listingProduct;
       $this->_collectionFactory = $collectionFactory;
       parent::__construct($context, $filter);
   }

   public function execute(){
     //$collection = $this->filter->getCollection($this->_collectionFactory->create()); // get your selected collection
     //$collectionSize = $collection->getSize();
     //echo $collectionSize;
     $data = $this->getRequest()->getParams();
     print_r($data['selected']);
     exit;
   }

   /**
    * @param AbstractCollection $collection
    * @return \Magento\Backend\Model\View\Result\Redirect
    */
   protected function massAction(AbstractCollection $collection)
   {

   }

}