Ook, thanks for the reply.
Could you can give me some hints on how is implemented the array2String function to understand what's wrong. I tried to implement one on my own and it worked.
If it's possible. thank you .

Hi, I have I problem testing my code in C.
Maybe I did something wrong but the function array2String function gets an INVALID MEMORY ACCESS while testing. The weird thing is that if I comment out the call to array2String and print the array... it works without problem. Could you please help me?

With Char codes: 'Y'(89) + 2 => '['(91) that could be right if a simple +2 shift is required
3rd request makes circular shift obvious for the function to be reversible.
Specifing Circular Shift would make easyer to understand at first look, but that's not really necessary.
Just a suggestion to make it clearer.
Good Kata ;)

Explicitly say that shifting letter is circular ( y + 2 -> a ) could make easiear to understand what to do at first glance

I'm trying to submit my code but tests fail. If I console.log() my responce is right but Test says return value is not. It seems to match another's test return value. May be some mess with tests order? Or I've done something wrong ( that's possible too ;) )

In the description cellphone object is assumed to be an object with tho strings: owner and number.
Owner is not a string but a Person instance.

First:
Missing check for a single last number while saving:
Test.assertEquals(createRangesString('1,2,3,4,5,7,8,9,11'),'1-5, 7-9, 11' );
My first try failed with such string but it let me save even if the algorythm was failing with a single last number.

Second:
in the description you use function named minimiseString(str) but into code function's named createRangesString(str). Just a minor thing but this could be a bit confusing.