Louis Spohr, a German violinist and composer in the 1800s, has been considered as the equivalent of Paganini in the clarinet repertoire because of the sheer difficulty of his clarinet works.
He wrote them as they were to be played on the violin. For this reason, the musical motifs in his concertos tend to be quite long and require a careful breath control. Maintaining the intonation can also be really difficult. Some people circular breathe (i.e., breathe while playing) to cope with their shortness of their air capacity.
Here’s my attempt of the First Movement of Spohr’s Concerto No.1.