@Test( expected = UnsupportedOperationException.class )
public void shouldReturnImmutableIteratorOfChildren() {

    parent = new PlanNode(Type.JOIN);
    new PlanNode(Type.ACCESS, parent);
    new PlanNode(Type.DUP_REMOVE, parent);
    new PlanNode(Type.GROUP, parent);
    Iterator<PlanNode> iter = parent.iterator();
    iter.next();
    iter.remove();
}