Gday Sunny,
In my experience, unless you, the owner/builder, are really experienced and current on the same type of aircraft - Don't test fly it
If you look up EAA/FAA accident records, you'll find a disproportionate number of incidents/accidents directly involving the low time/low experience owner/builder. The higher the performance of the aircraft = the greater the need for the TP to be truly competent.
I've seen a builder nearly cook the aircraft on its' very 1st engine start because he had no idea on handling FI/EI fitted Lycomings. Another started up and only then found the brakes had not been checked = damaged aircraft. And there are many more.
Read up on 1st flights and Phase 1 flight testing and do your part by ensuring the arrangements are all in place for your 1st flight. eg, weather is calm, traffic is light, airport management knows what's about to happen,paperwork complete,and so on according to the AP approved plans.
A TP with type experience has a fair grasp of how the engine and airframe will feel or indicate - so don't be surprised if the flight lasts 10 mins and he's back with a comment that something doesn't appear safe. You might have several short flights to get adjustments made to controls to airframe or engine - but that's why you have a TP.
Enjoy it and good luck. p