Testing Grounds is the fourth Soviet mission in Aftermath to steal a new vehicle, but try to destroy an Allied base quietly from overhearing any enemies coming their own ways.
Soviet Premier, Josef Stalin congratulated Field Commander S7 for stealing the Allied vehicle in the previous mission despite military efforts to find out what it is. A Spy tells Stalin the information of a Phase transport to be the likelyhood of the Allied plans. Stalin was curious to find out why the Allies did that and asks Field Commander S7 to steal this vehicle and travel to disrupt Allied communication systems plus stealing some experimental plans, before sending in a force to destroy this enemy base of operations in Europe.
Following the confrontation, Stalin immediately congratulated the Commander for a job well done. The Phase transport was now in Gradenko's hands to work on and now the Commander is told by Stalin that some naval forces of the Allies are coming to attack.