Missing fixed and example tests:

• s = t = "ABCDEF and t being a permutation of s
• s,t = "ABSDGFDHKDFHA", "AA"
• s,t = "AABSDGFDHKDFH", "AA"
• s,t = "BSDGFDHKDFHAA", "AA"

The random tests should also generate more versatile inputs. t inputs are currently very long, meaning the tests will in the end almost always generate the same kind of situations (confirmed when I was playing in forks: I very often got all the fixed tests wrong, and all the random tests passing, or just 1 wrong). So, the generation should pick different strategies randomly:

• the current one
• the current one, but enforcing very short t (length < to 5 or 10)
• pick a substring of various length in the generated s
• pick a substring of various length in the generated s, at the beginning or the end

cheers

Hi,

• Missing a batch of small random tests
• the description is not clear about XYYT being considered or not a possible substring for XYT. Edit: as a matter of fact, it seems to be valid => missing sample and fixed test, also.
• Also, don't define the ref solution at each iteration in the random test.

Cheers

Potential copyright infringement: https://leetcode.com/problems/subarray-sum-equals-k/.

[8, -8, 9, 10] 0
6 should equal 1

I don't see anything about excluding empty subarrays in the description.

If the substring does not exist, simply return an empty substring.

A return value of an empty substring would also be a valid answer to a valid possible input ( empty t ), so is a less than ideal choice for "no substring possible." Consider asking for None instead.

No random tests https://docs.codewars.com/authoring/guidelines/submission-tests#random-tests

It looks in the description like m and n are arguments as well. It would be more clear to specify you will receive a square matrix, and leave its dimensions to be determined by solver.