Prado\Collections\TPriorityList::add PHP Method

    public function add($item, $priority = null)
    {
        if ($this->getReadOnly()) {
            throw new TInvalidOperationException('list_readonly', get_class($this));
        }
        return $this->insertAtIndexInPriority($item, false, $priority, true);
    }

 public function testOffsetUnsetTPriorityList()
 {
     $list = new TPriorityList();
     $list->add(2);
     $list->add(1, 5);
     $list->add(3, 15);
     $list->offsetUnset(1);
     self::assertEquals(array(1, 3), $list->toArray());
 }