class_docstr: Basic tests on the util functions in TorchAgent.
class_docstr_tok: ["Basic","tests","on","the","util","functions","in","TorchAgent","."]
code: def test_truncate_metrics(self):
      agent = get_agent(model="test_agents/unigram", truncate=5)
      obs = {
          "text": "I'll be back. I'll be back. I'll be back.",
          "labels": ["I'll be back. I'll be back. I'll be back."],
          "episode_done": True,
      }
      obs = agent.observe(obs)
      agent.act()
      self.assertEqual(agent._local_metrics["ctrunc"][0].value(), 1.0)
      self.assertEqual(agent._local_metrics["ltrunc"][0].value(), 1.0)
      self.assertEqual(agent._local_metrics["clen"][0].value(), 9)
      self.assertEqual(agent._local_metrics["llen"][0].value(), 11)
      self.assertEqual(agent._local_metrics["ctrunclen"][0].value(), 4)
      self.assertEqual(agent._local_metrics["ltrunclen"][0].value(), 6)
  
imports: import os
  import unittest
  from parlai.core.agents import create_agent_from_shared
  from parlai.utils.testing import tempdir
  from parlai.utils.misc import Message
label_desc: Use image node_id 20 for calling the TestTorchAgent obj's underlying member method code with example usage: obj.test_truncate_metrics() without return types