Looks like secret tests are working differently: main class is not unloaded each time.

The most confusing is

The return value of the method is changed based on the registered callback

I've payed a lot of time to understande expected behavior from tests. Please describe it more accurate inside Instructoins.

It works, but it ignores:

Refactor the function into a recursive Fibonacci function that using a memoized data structure avoids the deficiencies of tree recursion Can you make it so the memoization cache is private to this function?

It works, but it ignores:

Refactor the function into a recursive Fibonacci function that using a memoized data structure avoids the deficiencies of tree recursion Can you make it so the memoization cache is private to this function?

Be my guest! :D

May i please reuse your library in the future katas?

This is how this kata should be sovlved for real without cheats like Array.permutation!

Looks clever, but I really can't read it.

looks OOPish