value are not set by the calling function in mocha framework

i have written random function to set some string values in accountname and this is in utilities/random.js. when I try calling this function in my test/sample.js this function is not setting the value of account name

random function

export const randomString = (n) => {
    let str = 'abcdefghijklmnopqrstuvwxyz9876543210';
    let tmp = '',
        i = 0,
        l = str.length;
    for (i = 0; i < n; i++){
        tmp += str.charAt(Math.floor(Math.random() * l));
    }
    return tmp;
}

calling it in test/sample.js

import { randomNum, randomString } from '../utils/random';     
let accountname = randomString(length);