Hello,
I noticed there was a coop option for Test Track and it wasn't what I was expecting it to be. I was hoping it be where the host picks a car to work on with their buddy and during load up the host's car is the one that will be worked on. The upgrader will be the buddy that chooses the parts and installs them on vehicle and once they're done a popup window will appear to confirm the new parts installed for the host. This will bring a more team effort into car tuning and upgrading while the host test the new upgrades and tunes.