code: def test_text_history_last_segment(self):
      text = "Hello there!"
      tokens = torch.tensor([1, 2, 3])
      history = TextHistory(text, tokens)
      history.append_segment("General Kenobi!", torch.tensor([4, 5, 6]))
      history.append_segment(
          "You are a bold one!", torch.tensor([7, 8, 9])
      )
      self.assertEqual(history.last_text_segment, "You are a bold one!")
  
imports: import unittest
  from unittest.mock import patch
  import torch
  from transformers import AutoTokenizer
  from trl import AutoModelForCausalLMWithValueHead, TextEnvironment, TextHistory
label_desc: Use image node_id 4 for calling the TextHistoryTest obj's underlying member method code with example usage: obj.test_text_history_last_segment() without return types