What are the advantages and disadvantages of mandtory vs voluntary HIV testing?

In what setting? I can give you only the most general answer: when testing for a stigmatized condition is mandatory, those at highest risk often find ways to avoid the test because of perceived punishment. Voluntary testing allows people concerned about their own risk to come forward and take responsibility for the test--and its outcome. Proponents of mandatory testing often are concerned about thoroughness. Proponents of voluntary testing often are concerned about giving results to people who are ready to hear them. In most environments, it's a question of the choice between the carrot and the stick. I can't say more without knowing something about context.