Thanks! But is the trailing loco being used for traction? In case of testing locos, I have usually seen that both the locos are MU'ed (MU cables connected), but only one of them supplies traction, and the other one is powered up only in the event of a failure.
A similar arrangement happens with TPTY-MTM/NS express train. It gets twin WDP1 locos from BZA to GDV, where the train bifurcates. The twins continue with one portion, while a separate WDP1 is stationed at GDV for the other portion. I used to think that the MU'ed locos themselves were separated at GDV to haul each portion, until I found that MU'ing is usually done only at Loco sheds.