Yep, I know and already provided another solution.
The thing is that there is no check for odd number of the same letter in this Kata.
That's why I proposed to add 'aaa' test case.

Hi!
It would be great to add test cases like 'aaa', 'aa' and 'a'.
I found a solution which could pass all tests, but can't handle 'aaa', 'aa' and 'a'.

Seems that test cases were chaged after this solution.
'http://google.co.jp' returns 'co' instead of 'google'

That's why I ask to add such test case to avoid accepting non universal solutions.

What do you think about adding sum_pairs([12, 4, 5, 3, 8, 7, 5, -2], 10) in test cases?
In such dataset you can find 3 nested pairs: [12,-2], [5, 5], [3, 7] where [3, 7] is the right pair.

The thing is, that I wrote solution, which passes all tests and successful at attempt, but can't handle provided dataset because it has 3 nested pairs.
Including sum_pairs([12, 4, 5, 3, 8, 7, 5, -2], 10) will help avoid wrong solutions.

Try to solve it without "for" or "while". Attention: can blow your mind.