Agh, I edited the description (just the other day) per someone else's recommendation and didn't spot that! Fixed.

Amended the description - hopefully to make it better.

I'm curious why this would classify as a puzzle - I thought it would be pretty simple fetch-info-from-object kata...

This may be me solving this later in the evening, but the example test cases imply that it is the last letter of the word that is being repeated twice and then has "k" added.
You may want to consider adding a test case which makes the actual rule more obvious. :)

Hi, thank you for your comment. This is my first kata, so I'm not surprised it has an many holes as Dutch cheese!

I swapped the Test.assertEquals to assertDeepEquals.

Issue with blue - fixed - Originally I spotted that and fixed it in one of the test windows, but not the other.

Hardcoded solution - mistake at my end, had a wrong number in my code, fixed that.

Thank you for your feedback, it's valuable for a beginner. :)

Ah, silly me, had one number wrong. Thanks for pointing it out! Fixed.

You may want to consider changing "should not use loops" to "must not use loops". First discurages using loops, but I would expect the code to pass all tests. "Must not" would make it clear that a loop in the code would fail the test.