def test_data_is_retained(self):
expected = TreeNode("4", None, None)
bst = BinarySearchTree(["4"])
self.assertTreeEqual(bst.data(), expected)
def test_smaller_number_at_left_node(self):
expected = TreeNode("4", TreeNode("3", None, None), None)
bst = BinarySearchTree(["4", "3"])
self.assertTreeEqual(bst.data(), expected)
