how to write unit test for this class in JUnit

Question

//how to write unit test for this class in JUnit......

package com.emr.common.helper;

import java.util.Random;

public class RandomTextGenerator {

    public static String getAutogenerateText()
    {
        /*Auto genarate password    */

        String password = "";
        /* Create Auto Password */
        int count = 36;
        // int range = Integer.MAX_VALUE;
        int sum = 0;

        Random rand = new Random();
        for (int j = 0; j < 45; j++) {
            for (int i = 0; i < count; i++) {
                sum = rand.nextInt(count);

            }
            char[] pass = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
                    'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
                    'W', 'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7',
                    '8', '9' };
            password = password + pass[sum];
        }

        return password;
    }

}

Answer 1

You won't be able to effectively test this class if you say new Random() - by doing this you have hard-coded a reference to what is effectively an external dependency (a source of random numbers) which you can't control.

Instead you should pass a Random object into the class via a method argument, and supply a mock implementation in your test for which you can control the values that get returned.

Answer 2

Try to match it against an RegEx which checks if the returned String matches 45 characters mixed of Letters and Digits.

This RegEx should work:

^[A-Z0-9]{45}$