One can actually inherit from an inner class. It's a little very wordy, but it should work

Test information is .. sparse. The tests really could use better messages

Please describe what exactly is meant by "rotation" it's not clear from the context and word alone.

Also test-cases don't give nice information about what went wrong.

Oh sorry... I was talking about java

I personally find the index solution somewhat cramped and clunky. I'll need to revisit this later. This can definitely see some improvement on the caching and lazy loading part.

This kata needs an overhaul. test-cases don't check for an incorrect return of 10, and the method shouldn't be named in snake_case....

The parameter names could use a little improvement.
The requirement of an empty string should IMO be pronounced a bit more, possibly by adding it to the initial test suite.

Aside from that, very nice challenge

Hello There,

I have gotten this kata to pass all test-cases but the last one.
I personally think skipping 3mil. Items in a ORDERED Stream in less than 10 seconds is a too heavy performance requirement :(

Then on the other hand I am not that good at performance intensive Programming.

If the goal of this Kata is primarily to focus on the performance aspect of calculating primes, that's awesome.
If the goal is to properly leverage Streams, then the last test case is too brutal for this kata.

Very interesting Kata, though, thank you