JUnit Test for Java

Question

如何为下面的方法编写JUnit测试？

private static final String CHAR_LIST = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";

    private int getRandNum() {
         Random getRand = new Random();
         int randomNum = getRand.nextInt(CHAR_LIST.length());
         if (randomNum == 0) {
              return randomNum;
         } else {
              return randomNum - 1;
         }
    }