Overseas Travel between Australian Citizenship Test and Ceremony.
If you travel outside Australia before your Australian Citizenship ceremony, it will be as a permanent resident.
You can only use the passport of the country of which you are currently a citizen, and you must have a valid travel facility on your permanent visa so that you are permitted to return to Australia with your permanent resident visa.
It is highly advisable to notify immigration of your travel plans, so they can delay your ceremony until after your return.