test_iterator.py

from unittest import *

class Node:
  def __init__(self, value, left=None, right=None):
    self.right = right
    self.left = left
    self.value = value

    self.parent = None

    if left:
      self.left.parent = self
    if right:
      self.right.parent = self

  def traverse_preorder(self):
    def traverse(current):
      yield current
      if current.left:
        for left in traverse(current.left):
          yield left
      if current.right:
        for right in traverse(current.right):
          yield right
    for node in traverse(self):
      yield node.value

class Evaluate(TestCase):
  def test_exercise(self):
    node = Node('a',
                Node('b',
                     Node('c'),
                     Node('d')),
                Node('e'))
    self.assertEqual(
      'abcde',
      ''.join([x for x in node.traverse_preorder()])
    )