Dear Parwinder, Australia accepts the scores of IELTS, TOEFL, iBT, PTE Accademic, CAE and OET for studying in Australia.The test that you need to take depends upon your current situation. If you need to appear for an exam in very short period of time as you have to start your course immediately, then PTE is the ideal choice. The Pearson Test of English gives you results in 5 days. If you have plenty of time, hen it is Cambridge English Advanced Test which gives results in 6 weeks. For IELTS, the minimum required score is 5.5. For TOEFL, its 46,  for CAE it is 162, PTE Accademic it is 42 and OET is Pass A or Pass B.  Regarding the mandatory subjects can you let us know which course do you want to study in Australia?