code: def test_ppl(self):
      valid, _ = testing_utils.eval_model(
          {
              "model": "transformer/generator",
              "model_file": "zoo:tutorial_transformer_generator/model",
              "task": "dailydialog",
              "skip_generation": "true",
              "num_examples": 512,
              "batchsize": 32,
          },
          skip_test=True,
      )
      self.assertAlmostEqual(valid["ppl"], 19.59, places=2)
      self.assertAlmostEqual(valid["token_acc"], 0.4235, places=4)
  
imports: import unittest
  import parlai.utils.testing
label_desc: Use image node_id 1 for calling the TestTutorialTransformerGenerator obj's underlying member method code with example usage: obj.test_ppl() without return types