In Victoria there is now rre-test for your bike license, you simply change it with your driving license and there's theory test either.
If you have any form of HGV license though you do have to sit theory and hazard tests as well as doing practical driving tests. There are 5 classes of HGV out there and a class 1 here will allow you to go straight for the top class license in Victoria at least.
Been doing homework on this one cos Michael needs to drive for a living (we think!) and had responses along the above lines from various companies that do the testing.
Felicity
