I worked at a main VAG dealer back in the 80's, at that time a compression test was a routine part of the main service (every 12,000 miles)
I cannot remember the temperature of the engine being a consideration when carrying out the compression test. However, having said this I guess it makes more sense for it to be at least warm so the oil is thinner and so the engine spins more freely etc, I suppose you are also less likely to flatten the battery as the compression gauge will max out more quikly.
Martin
On wings like angels whispers sweet
my heart it feels a broken beat
Touched soul and hurt lay wounded deep
Brown eyes are lost afar now sleep xxHayleyxx