True, and thanks for your suggestions. I suspect that given this kata is rated at 42%, it will never see the light of day outside of beta, so it might be a lost cause now.

I completely agree. Sorry to the user that did that before it was prohibited :/

The tests should be working correctly.

Python translation was broken because it relied on file concatenation that we previously did internally.
I've just fixed this by including the class declaration in the solution.
Try resetting or start from the following:

class Cons:
    def __init__(self, head, tail):
        self.head = head
        self.tail = tail
      
    def to_array(self):
        return [self.head] + (self.tail.to_array() if self.tail is not None else [])
      
    @classmethod
    def from_array(cls, arr):
        #TODO: convert a Python list to an algebraic list.
        pass
    
    def filter(self, fn):
        #TODO: construct new algebraic list containing only elements
        #      that satisfy the predicate.
        pass
    
    def map(self, fn):
        #TODO: construct a new algebraic list containing all elements
        #      resulting from applying the mapper function to a list.
        pass

This invalidated many solutions, but it's better than having broken translation.

I think that the string is not trimmed in random tests:
Expected: equal to muIcKiTXBKIdGdTwFMFnAxdtEUrRClWvsMPdJxay lPduzTkLMLxay
Actual: muIcKiTXBKIdGdTwFMFnAxdtEUrRClWvsMPdJxay lPduzTkLMLxay

After adding char in front and in end
Expected: equal to PIPay
Actual: PIPay

Possibly. I was thinking 4kyu when I first devised this kata, but a couple of other people assessed it at 3kyu and 2kyu.

could the difficulty depends on the language? Because, just look at alexshavlovsky's comment below (doing java)

if so, that's bad and the version you did should be updated with more demanding tests.

Fixing the tests is what I think is best (so all languages behave the same).

Punctuation marks shouldn't be inside words, they should be separated by spaces like in other languages.