### Question:
MerkleTree { public Leaf leftLeaf() { return (leftLeaf); } MerkleTree(MessageDigest md); void add(final MerkleTree leftTree, final MerkleTree rightTree); void add(final Leaf leftLeaf, final Leaf rightLeaf); MerkleTree leftTree(); MerkleTree rightTree(); Leaf leftLeaf(); Leaf rightLeaf(); byte[] digest(); void prettyPrint();  }### Answer:
@Test public final void testLeftLeaf() { Leaf leftLeaf = leafTree.leftLeaf(); assertTrue(leftLeaf.toString().equals(leftLeafString)); }