This solution is awesome but I don't understand it at all. I can understand how the split separates by odd numbers. But I don't understand why it doesn't remove the separator characters (i.e. why odd numbers don't get removed) and why it generates empty characters after each odd.

Yup :)

There does seem to be an issue with ruby random tests.

Are they not working?
They should work fine.

Are the random tests working for the Ruby Kata?

Right. "Partner" instead of "girlfriend" would be a quick and easy fix. Representation is important, espcially since software development is, statistically speaking, not very inclusive.

This kata, for at least Python, is harder than an Eight.

It would be nice to update this one to be less gender-presumtive.

Nice guard clause at the top :)

That is 'stabby' lambda sytax.

->(n) { n }

is the same as

lambda { |n| n }

this is the ES6 way ;)