import java.util.Collections;
import java.util.List;

import com.google.common.collect.Lists;
import com.google.common.primitives.Ints;

public class IntArray {

    public static int[] ofSize(int size) {
        if (size < 0) throw new IllegalArgumentException(
                String.format("Expected a size [%d] to be at least 0", size));
        List<Integer> ints = Lists.newArrayList();
        for (int n = 0; n < size; n++) ints.add(n);
        Collections.shuffle(ints);
        return Ints.toArray(ints);
    }
}

import java.util.Random;

import org.junit.Test;

public class IntArrayTest {

    @Test public void ofSizeIsRandom() {
        Random randomizer = new Random();
        int size = randomizer.nextInt(1000) + 2;
        int index1 = randomizer.nextInt(size), index2;
        do index2 = randomizer.nextInt(size); while (index1 == index2);
        int value1 = randomizer.nextInt(size), value2;
        do value2 = randomizer.nextInt(size); while (value1 == value2);
        int round = 1;
        do {
            int[] ints = IntArray.ofSize(size);
            if (ints[index1] == value1 && ints[index2] == value2) break;
            int threshold = size * (size - 1);
            if (round % threshold == 0) {
                System.out.println("perhaps the function does not produce random arrays");
            }
            round++;

        } while (true);
    }
}