DragAgent
From Documentation
DragAgent makes you mimic dragging a component and drop on another component. You have to query the component you want to drag first and convert it as DragAgent then call dropOn(ComponentAgent) . The argument you pass into the method is the target component you want to drop on.
The following code presents how to drag a listitem from left listbox to right listbox.
//move 1 item from left to right
ComponentAgent draggedItem = leftBox.query("listcell[label='ZK Forge']").getParent();
draggedItem.as(DragAgent.class).dropOn(rightBox);