I think they are BSing you a bit here on compression testing..
I mean you wont get a final result but you will get a TELLING reszult...ie you have a bad cylinder, or you have them all pretty close.. , you have very little compression, ot you have quite a lot..
If you have even medium compression (or any) it will probably run, , if it runs for a while, it will probably go up.
But if it has very little, then you may be looking at a lot fmore work on it, ie tearing apart..
Fairly simple.... but can be turned into complicated by some...imo..