Testing 1,2,3
Let's begin by saying that you should never buy any vehicle that you have not tested. A test drive or ride will let you know if the vehicle has any idiosyncrasies that may become an issue later on. The type of test will also depend largely on the type of vehicle being purchased and the type of driving that will be done with said vehicle.
Related: Should you always test drive a car?
It won't do you much good to test an offroad biased vehicle in heavy traffic during rush hour when you are buying it for weekend overlanding nor will it do yourself much good driving a small hatchback on a heavy gravel road. So what then is the best way to test drive a car?
Type of vehicle
The type of vehicle that you are planning to test will dictate the type of test drive you take. For a sports car, wou will want to test its handing and power delivery so an open road or freeway will suffice. For 4x4 type vehicles you will want to at leas find some dirt or offload to test the suspension and 4x4 systems.
Type of driving
The type of driving that the vehicle is going to do predominantly will also dictate the type of test you should do. If you are bound to the suburbs and just doing a shop and school run then try to do some driving in a parking area and quiet suburban back roads.
Combined cycle
The best type of test drive you make is to test all of these in the same test, but that will not always be possible. The combined cycle refers to a dual test wherein the vehicle is tested on both open and city roads. You should drive on eth freeway at speed and also include some stop-start traffic driving to ensure that the vehicle is up to your expectations.