def test_can_successfully_return_a_collection_from_a_postorder_traversal():
new_tree = BinaryTree()
new_tree.root = Node("A")
new_tree.root.left = Node("B")
new_tree.root.right = Node("C")
new_tree.root.right.left = Node("F")
new_tree.root.left.left = Node("D")
new_tree.root.left.right = Node("E")
expected = ["D", "E", "B", "F", "C", "A"]
actual = new_tree.postOrder()
assert expected == actual
def test_6 ():
node1 = TNode(1)
node1.left = TNode(2)
node1.right = TNode(3)
node1.right.left = TNode(5)
node1.right.right = TNode(4)
node1.left.right = TNode(6)
node1.left.left = TNode(7)
binary_tree = BinaryTree(node1)
actual = binary_tree.postOrder().__str__()
expected = '-> 1 -> 3 -> 4 -> 5 -> 2 -> 6 -> 7 -> None'
assert actual == expected