How to shorten a string by n characters in a Ruby array?

Question

ruby

Hello.

I have one array which consists of data like "TestA: TestA, TestB: TestB" (It is divided into : and ,).
Data is read and output using the map_array function (map_array['TestA']).

The question is how to shorten a string from an array by n lines. That is, I would like to get map_array['TestA'] = Tes (for example). But at the same time without touching the array itself.