### Question:
Tree { public List<Character> inorder() { List<Character> inorder = new ArrayList<>(); inorder(root, inorder::add); return inorder; } Tree(Node root); List<Character> inorder(); List<Character> preorder(); List<Character> postorder();  }### Answer:
@Test public void inorder() { Tree tree = new Tree( new Node( 'C', new Node('B', new Node('A'), null), new Node('E', new Node('D'), new Node('F')))); assertThat(tree.inorder()) .containsExactly('A', 'B', 'C', 'D', 'E', 'F'); }