Testing is manual and physical.
You can't test a new plane via software whose behavioral characteristics are not know and only theoretically predicated.
Simulation software will also be developed during this stage that will be used during weapons integration and testing.
there is a LOT of items to be tested and verified in a new airplane - that too as complex as AMCA
dont underestimate the process of learning through these tests
everyone we take a short cut and import an item, it adds to the tech debt of having to learn it form scratch but 10-20 years later- when other countries will be working on 3rd or 4th gen stuff.
I understand flying the real jet in air can only be predicted in sims &testing has to be done in multple environments, time, altitude, etc. But AMCA has the same typical tandem bi-plane design & MK1 with GE414 engine won't have TVC.
S/w coding also evolves with time. We are in era of machine-learning & AI. Perhaps some changes can be done on-the-fly like changing limits of actions & responses of control surfaces, etc.
Anyways i hope 5 years doesn't stretch. The Chinese surprised everybody twice with J-20 & J-35, now we have to do something fast.