@Override
    public long footprint() {
        return footprint;
    }
@Test
    public void testFootprint() {
        MerkleTree merkleTree1 = new ArrayMerkleTree(3);
        MerkleTree merkleTree2 = new ArrayMerkleTree(3);

        for (int i = 0; i < 10; i++) {
            merkleTree1.updateAdd(i, i);
        }

        for (int i = 0; i < 100; i++) {
            merkleTree2.updateAdd(i, i);
        }

        assertEquals(merkleTree2.footprint(), merkleTree1.footprint());
    }