You will always find some difficult passages in Leos Janácek’s works. Two examples are a) in the opera “The Cunning Little Vixen”. Commencing at the Allegro after Fig. 4 Act 1 there are 31 bars of harmonics for one bass solo and following that 2 bars 4/4 before fig. 29 there is a long difficult passage.
b) In the opera Katya Kabanova there are a couple of bars bass solo that are a trifle difficult. I forget exactly where they are but you can find them easily by perusing the score You would do well to find both of these excerpts and put them in your scrap book as they have come up occasionally in bass auditions for principal bass positions in opera orchestras. Some conductors like to catch you off guard so be prepared!