def test_basic(self):
     tree = TreeNode(
         4,
         left=TreeNode(1, right=TreeNode(2)),
         right=TreeNode(7, left=TreeNode(5), right=TreeNode(8))
     )
     self.assertLessEqual(nodes_at_depth(tree, 2), [2, 5, 8])
 def test_single(self):
     tree = TreeNode(5)
     self.assertEqual(nodes_at_depth(tree, 0), [5])
     self.assertEqual(nodes_at_depth(tree, 1), [])
 def test_simple(self):
     tree = TreeNode(4, TreeNode(1))
     self.assertEqual(nodes_at_depth(tree, 0), [4])
     self.assertEqual(nodes_at_depth(tree, 1), [1])
     self.assertEqual(nodes_at_depth(tree, 2), [])