I've tried to spawn Testacles the Debug Centurion by typing

prid 00139b8b

in the console. I was going to type

moveto player

after that. But no luck... Can't he be spawned with the prid command? Thanks in advance.

You need to use his Reference ID, not Base ID if you plan to use Prid.

To spawn him with Base id, use player.placeatme [BaseID] 1