Since they can be in any order it makes really hard to predict in which part will be the correct letter and still we've to take care of duplications, the Kata tried to make things hard but it makes no sense at all since the input and part1 and part2 can vary so much that's pretty hard to cover all the situations.

Why the test should pass for: "Bannas from Bahamas"
part1: Bahas
part2: Bananas from am

When it reaches the "h" we can see that it's out of order: "The restriction is that the characters in part1 and part2 should be in the same order as in s"

An example of how it should be:
s: c o d e w a r s = codewars
part1: c d w = cdw
part2: o e a r s = oears

Yes, I notice this right now my code is right but the test won't pass, that's pretty frustrating.

Thank you so much man, I was struggling very hard here and you saved me.