### Question:
UniqueNumbers { public static int treeSize(TreeNode root) { if (root == null) { return 0; } return 1 + treeSize(root.left) + treeSize(root.right); }  static void main(String[] args); static void printTreeAscending(TreeNode root); static void printTreeDescending(TreeNode root); static TreeNode addNode(TreeNode root, int value); static int treeSize(TreeNode root); static boolean containsValue(TreeNode root, int value);  }### Answer:
@Test public void testSizeOfEmptyTree() { assertEquals(0, UniqueNumbers.treeSize(null)); }
@Test public void testSizeOfRoot() { TreeNode root = new TreeNode(); assertEquals(1, UniqueNumbers.treeSize(root)); }