Adrenaline can improve function in a number of domains, so it might be that anyone who has test anxiety or some other performance anxiety could in certain situations that they perceive as threatening have some sweet concentration of adrenaline in their bodies such that they have improved performance rather than impaired performance, and this is never recognized as occurring by the same mechanism as test or performance anxiety unspecified because the amount of adrenaline causes symptoms that aren't detrimental. Conceivably the amount of adrenaline and the effects thereof could be different across different domains.

Maybe that happens to you. What do you think?

EDIT: This might lead to empirical evidence. Anxiety may decrease performance when attention has to be switched between tasks, but may improve performance when the task is difficult and singular. Think social situations vs. exams.