Paganini again: the finale of his Second Concerto, played by Alexandru Tomescu. It’s nicknamed La Campanella for the little bell that rings in the orchestra, answered by the violin in harmonics. Most people know it as Liszt’s piano étude, which says something about how often the original gets played.
Is it hard? Yes: harmonics, double-stop harmonics, ricochet, leaps across the fingerboard, all fully exposed. But it’s a different kind of hard from Brahms or Tchaikovsky. One tune comes back again and again, each time with a new trick. The orchestra mostly goes oom-pah. There’s no forty-minute structure to hold together. Paganini was friends with Rossini, and you can hear it: this is an aria, and the violin is the soprano.
So I think it’s less a test than a status symbol. Plenty of students play it with piano. The hard part is getting a major orchestra to play the oom-pah for you on a serious program. Tchaikovsky proves you can play. Paganini with orchestra proves you’re worth accommodating.