There are now random tests. So this is probably resolved?

Challenging! Especially the possibility of a key's being int or string makes it even more compelling. Nice kata.

In the task n is said to be in range [3, 30], but random tests have examples with n==1.

In my opinion "a range of numbers" is an ambiguous description. Your examples show a range of consequitive numbers, and the Kata you are extending also uses the word "consequitive." It would be great if the description made that clear.

Ahh you're right :) my mistake

This is okay, because of this part of the kata description:

The terms of a subsequence need not be consecutive terms of the original sequence.

There's a small mistake in the description section of the python translation of this kata:

Example subsequence

Subsequences of "abc" = "a", "b", "c", "ab", "ac", "bc" and "abc".

"ac" is not a subsequence of "abc" :)

Lack of small preloaded tests, especially tests on arrays.
Debugging huge random tests is quite a pain.

see above (manual notification)

Hey :)
I've added random tests now - sorry about before I really misunderstood what was meant by random! Let me know if you think the test-cases help the strength of the kata - I'd love to get it published. I can keep investigating more efficient solutions too.

what about the possibility of having a list as first layer? (note: it would need a slight change in the description)

I just looked at the test suite and...

x/

those are not random tests, they are fixed tests. => look at some others katas you solved (recent one if possible) and study how the random tests are done.

Note: in your case, you'll have to compute the expected solution before you send the data to the user (or you'll need to make a deep copy of the structure)