I also thought that would be cool to solve this using regex!

In my case I used join('') enstead of join('-') and solved the /222/ problem by checking how many numbers are behind like this /^(...)*2{3}

You can see full code here:
https://www.codewars.com/kata/reviews/525caa5c1bf619d28c000338/groups/61e41f559a04f80001a6b80a

You have a most interesting flaw in your reinvention of Test.assertDeepEquals.

Also, what everybody already said + no random tests.

Needs serious change and improvement, or unpublishing.

Duplicate of this one: https://www.codewars.com/kata/merge-two-sorted-arrays-into-one

You should:

• either improve it with some new original idea/concept
• or unpublish it

Cheers

EDIT: actually, could rather be a duplicate of this one or something like that...

If you want people to write some code about algorithms, please improve your testcase to prevent brute force solutions. ;-)
And, example testcase missed.

So join('-') stops /222/ from solving your example as it add an extra character at the end of each row.