The C Broad Arrow is of course totally superfluous nonsense, but the "TEST" part may have some plausibility in that the cosmetic defect on the receiver wall MIGHT have caused a rifle or receiver to be pulled out of the production line. Long Branch maintained high standards of finish as well as quality.
On the other hand, the receiver looks like it has served long and hard, and if it was just a rejected receiver that later got built up post-war and slipped out the back door, it wouldn't show that much wear. The rare MkI cocking piece and early pattern safety lever also suggest it went through the production line in the usual way.
On balance probably all fakery.
Some of the worst wood butchery I've seen. Clown must have had access to a big belt sander and got carried away.