From my personal experiences, here are the things I have learned about using your own car or relatives car for driving test other than your driving instructor's car.
1. You can go for your road test in anyone's car as long as the car is insured properly, ownership papers and insurance documents should be located inside the vehicle at all times. Any accident claims will fall on the actual owner of the car but remember your own driving license record will still be affected in regards to demerit points.
2. As a G1 driver, you can not have your own auto insurance until you get your G2 driver's license, even if you own a car under your name. You will need to have someone who has 4 years of full license driving record sitting beside you when you drive. If you are going to the test centre, you need to have someone who has 4 years of driving experience beside you. You cannot go alone there. During the actual drive test time, the examiner will be the one who has more than 4 years of driving experience sitting beside you.
3. You do not need to put a "Beginner driver sign or board" on top of your car as mentioned by other people. Only driving school will have those signs on top of their car, not you.
4. What the drive test examiner will look for before the driving test begins are the car ownership papers, insurance slip papers, your drivers license card, no cracks on your mirrors, the left right indicator light is working, the brake lights at the back of car is working, your license metal plate is fine and not hanging loose, no serious physical damage on the car body that will prevent it from running on the road.
5. On the actual test date, you are required to arrive at least 30 minutes before your driving test. Check yourself in using the self serve kiosk located inside the driving test centre. You will need to enter your "Drivers License Number", "the exact parking spot number you parked your car in (This is so the examiner can locate your car fast and not waste time looking for your car)", "Your car license plate number (Doesn't matter whether it is your relative's car or driving instructor's car)". Once you are checked in, you need to immediately go and wait inside your car until the examiner comes and conduct a driving test for you. Remember to use washroom first, else you won't get another chance to use washroom later.
6. During the driving test, only you and the examiner can sit in your car. No other person are allowed on the behind seats.
7. If for whatever reason you need to cancel or reschedule your driving test, you should do so 48 hours before actual test date and time. Failure to do so, will result in cancellation fees.