"In my OPS manual it states that I have this responsibility from the moment I arrive on board to the time I get off "
WOW that took a very long time to get said and we need to believe you it is true.
LOL "I" consider I hope that's in your company ops to or you are probably off to jail or certainly wont be flying for a while!
No one can be forced to undergo CASA testing. However, refusing or failing to give a body sample may constitute a prosecutable offence. Further, anyone failing or refusing to give a body sample must stop performing or being available to perform an applicable SSAA. Failure to do so may result in a criminal charge.