code: def test_vacuum_nobackup(self):
      with testing_utils.tempdir() as tmpdir:
          from parlai.scripts.vacuum import Vacuum
  
          model_file = os.path.join(tmpdir, "model")
          valid, test = testing_utils.train_model(
              {
                  "task": "integration_tests",
                  "optimizer": "adam",
                  "learningrate": 0.01,
                  "model_file": model_file,
                  "num_epochs": 0.01,
                  "no_cuda": True,
                  "skip_generation": True,
                  "batchsize": 8,
                  # TODO: switch to test_agents/unigram
                  "model": "transformer/generator",
                  "ffn_size": 8,
                  "embedding_size": 8,
                  "n_layers": 1,
              }
          )
          size_before = os.stat(model_file).st_size
          Vacuum.main(model_file=model_file, no_backup=True)
          size_after = os.stat(model_file).st_size
          assert (
              size_after < size_before
          ), "Model file did not shrink after vacuum"
          assert not os.path.exists(
              model_file + ".unvacuumed"
          ), "Backup should not exist"
  
imports: import os
  import unittest
  from parlai.core.message import Message
  from parlai.core.mutators import MessageMutator, register_mutator
  import parlai.utils.testing
label_desc: Use image node_id 2 for calling the TestVacuum obj's underlying member method code with example usage: obj.test_vacuum_nobackup() without return types