When you say you want to sit the theory *test*, are you aware Oz uses more than one exam to cover their ATPL theory syllabus? There were four when I did mine nearly 20 years ago. The number of exams has varied over the years in approximate proportion to the number of name changes for the regulatory authority so damned if I know how many there are now.
CASA's website will have the details:
Civil Aviation Safety Authority - Home