A Game Effect of "...tests involving Willpower" seem to suggest that it work in far more situations than when just being exposed to interrogation, during natural recovery of stun damage and when resisting magic effects.
That fluff just give a few (open ended) examples supporting the crunch and is not to be seen as an exclusive (closed) list.
Having a mind that is hard to break could potentially also help you when opposing matrix actions, resonance actions, soaking matrix damage, opposing critter powers, the nauseated status, during composure tests, to avoid insomnia or the effects of loss of confidence, resisting a con, resisting toxins and drugs, etc etc as long as the test in question involve Willpower.
(Which also seem to include 'drain resistance tests').