JUnit Test that ArrayList elements aren't duplicates

Question

Using this method that generates an ArrayList using random values from a called method getRandomInt. What would I assert to create a test method that tests that the ArrayList doesn't contain duplicates?

public static int getRandom(int min, int max) {

    return random.nextInt((max - min) + 1) + min;
}

public static ArrayList<Integer> getRandomIntegers(int size, int min, int max) {

    ArrayList<Integer> number = new ArrayList<Integer>();

    while (number.size() < size) {
        int random = getRandom(min, max);

        if(!number.contains(random)) {
            number.add(random);
        }
    }

    return number;
} 

Answer 1

In fact you have to assert more than that.
To check the actual behavior of the method, you should indeed assert from the returned list that :

• the list has the expected size

Assert.assertEquals(size, list.size());

• the list doesn't contain dup

Assert.assertEquals(new HashSet<Long>(list).size(), actualList.size());

• the list elements are in the range min-max passed to.

for (long v : list){ Assert.assertTrue(v " + " is not in the expected range", v >= min && v <= max); }

As M. le Rutte underlined, I would also argue that the method API would make more sense to return a Set instead of List as an order of elements is not expected : the number are random.

And as a side note, your implementation is not efficient.
With a large range and a size requested close to the range size, you could loop much more than required.