              root.pre_order_traversal(sys.stdout.write)
              assert_equal(out.getvalue().strip(), '52138')
  
          with captured_output() as (out, err):
              root.post_order_traversal(sys.stdout.write)
              assert_equal(out.getvalue().strip(), '13285')
  
          root = Node(1)
          root.insert(2)
          root.insert(3)
 
</s> remove         root = Node(1)
        root.insert(2)
        root.insert(3)
        root.insert(4)
        root.insert(5)
 </s> add         node = Node(1)
        insert(node, 2)
        insert(node, 3)
        insert(node, 4)
        insert(node, 5) </s> remove             root.pre_order_traversal(sys.stdout.write)
 </s> add             pre_order_traversal(node, sys.stdout.write) </s> remove             root.in_order_traversal(sys.stdout.write)
 </s> add             in_order_traversal(node, sys.stdout.write) </s> remove             root.pre_order_traversal(sys.stdout.write)
 </s> add             pre_order_traversal(node, sys.stdout.write) </s> remove         root = Node(5)
        root.insert(2)
        root.insert(8)
        root.insert(1)
        root.insert(3)
 </s> add         node = Node(5)
        insert(node, 2)
        insert(node, 8)
        insert(node, 1)
        insert(node, 3)
            post_order_traversal(node, sys.stdout.write)
              root.pre_order_traversal(sys.stdout.write)
              assert_equal(out.getvalue().strip(), '52138')
  
          with captured_output() as (out, err):
            post_order_traversal(node, sys.stdout.write)
              assert_equal(out.getvalue().strip(), '13285')
  
          root = Node(1)
          root.insert(2)
          root.insert(3)
keep keep keep keep replace keep keep keep keep keep
 Simpilfied depth first search challenge. 
graphs_trees/tree_dfs/test_dfs.py