QuickSelect algo implementation in Java

QuickSelect.java

public class QuickSelect {
    
    // STATIC VARS
    static Random rand = new Random();
    
    /*
        Tests
        -----
    */
    public static void main(String[] args) {
        int[] testArr = new int[9];
        
        System.out.println("TESTING _WITHOUT_ DUPLICATES");
        for (int i = 0; i < testArr.length; i++)
            testArr[i] = i;
        
        for (int i = 0; i < testArr.length; i++) {
            shuffle(testArr);
            test(testArr, i);
        }
        
        System.out.println("\n\n");
        
        System.out.println("TESTING _WITH_ DUPLICATES");
        for (int i = 0; i < testArr.length; i++)
            testArr[i] = i / 2;
        
        for (int i = 0; i < testArr.length; i++) {
            shuffle(testArr);
            test(testArr, i);
        }
    }
    
    public static void test(int[] arr, int k) {
        System.out.println("arr: " + Arrays.toString(arr) + " | k: " + k);
        System.out.println("  -> kth elt: " + quickSelect(arr, k) );
    }
    
    /*    
        QuickSelect Algo
        ----------------
        - k \in [0, arr.length)
    */
    public static int quickSelect(int[] arr, int k) {
        return quickSelect(arr, 0, arr.length - 1, k);
    }
    
    public static int quickSelect(int[] arr, int lo, int hi, int k) {
        int pivotIdx = getPivot(arr, lo, hi); 
        
        int partitionIdx = partition(arr, lo, hi, pivotIdx);
        
        if (partitionIdx > k) {
            return quickSelect(arr, lo, partitionIdx - 1, k);
        }
        else if (partitionIdx < k) {
            return quickSelect(arr, partitionIdx + 1, hi, k);
        }
        
        return arr[partitionIdx];
    }
    
    public static int partition(int[] arr, int lo, int hi, int pivotIdx) {
        int pivotVal = arr[pivotIdx];
        swap(arr, hi, pivotIdx);
        
        int partitionIdx = lo;
        for (int i = lo; i <= hi - 1; i++) {
            if (arr[i] < pivotVal) {
                swap(arr, partitionIdx, i);
                partitionIdx++;
            }
        }
        
        swap(arr, hi, partitionIdx);
        return partitionIdx;
    }
    
    public static int getPivot(int[] arr, int lo, int hi) {
        return rand.nextInt(hi + 1 - lo) + lo;
    }
    
    public static void swap(int[] arr, int i, int j) {
        int tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }
    
    
    /**
        fischer-yates shuffle
        ---------------------
    */
    static void shuffle(int[] arr) {
        int len = arr.length;
        
        for (int i = 0; i < len; i++) {
            int j = rand_range(i, len);
            swap(arr, i, j);
        }
    }
    
    static int rand_range(int lo, int hi) {
        return rand.nextInt(hi - lo) + lo;
    }    
    
}