@JandE: I think you are completely right, I call DIBP and the operator said it is just important to be noted so that they would not arrange the ceremony during my travel, rather than that, nothing is important.I haven't seen anything about the test approval being unable to be done while outside Australia.
That could be quite important for some.
Thanks for you advice as well.
At least it cleared out my mind so that I can book the ticket now.
I hope to update my approval status soon.