      "def pre_order_traversal(node, visit_func):\n",
      "    # TODO: Implement me\n",
      "\n",
      "def post_order_traversal(node, visit_func):\n",
      "    # TODO: Implement me"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
 
</s> remove     "collapsed": false
 </s> add     "collapsed": true </s> remove     "%run ../utils/captured_output.py"
 </s> add     "%run ../utils/results.py" </s> remove     "%run ../utils/captured_output.py"
 </s> add     "%run ../utils/results.py"
    "    # TODO: Implement me\n",
    "    pass"
      "def pre_order_traversal(node, visit_func):\n",
      "    # TODO: Implement me\n",
      "\n",
      "def post_order_traversal(node, visit_func):\n",
    "    # TODO: Implement me\n",
    "    pass"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
keep keep keep keep replace keep keep keep keep keep
 Reworked tree dfs unit tests. 
graphs_trees/tree_dfs/dfs_challenge.ipynb