static int addHash(int originalHash, int addedHash) {
        return originalHash + HUGE_PRIME * addedHash;
    }
@Test
    public void testAddHashIsAssociative() {
        int hash = MerkleTreeUtil.addHash(0, 1);
        hash = MerkleTreeUtil.addHash(hash, 2);
        hash = MerkleTreeUtil.addHash(hash, 3);

        int hash2 = MerkleTreeUtil.addHash(0, 3);
        hash2 = MerkleTreeUtil.addHash(hash2, 1);
        hash2 = MerkleTreeUtil.addHash(hash2, 2);

        assertEquals(hash2, hash);
    }