Writing a JUnit test for a random number generator

Question

I have a method which returns a random number between 0 and 10.

public int roll(){
    int pinsKnockedDown = (int) (Math.random() * 10);
    return pinsKnockedDown;
}

How would I write a JUnit test for this? So far I have put the call in a loop so it runs 1000 times and fails the test if - the number is less than 0 - the number is more than 10

How can I test that all the numbers aren't just the same, i.e.

Answer 1

Randomness tests are potentially complex. e.g. in the above do you simply want to ensure you get numbers between 1 and 10 ? Do you want to ensure a uniform distribution etc.? At some stage I would suggest you want to trust Math.random() and simply ensure you haven't screwed up the limits/range, which is essentially what you're doing.