code: def test_untar(self):
      with testing_utils.tempdir() as tmpdir:
          import io
          import tarfile
  
          zname = os.path.join(tmpdir, "test.tar.gz")
          with tarfile.open(zname, "w") as zf:
              with io.BytesIO(b"Test1\n") as f:
                  tarinfo = tarfile.TarInfo("test1.txt")
                  tarinfo.size = 6
                  zf.addfile(tarinfo, fileobj=f)
              with io.BytesIO(b"Test2\n") as f:
                  tarinfo = tarfile.TarInfo("test2.txt")
                  tarinfo.size = 6
                  zf.addfile(tarinfo, fileobj=f)
  
          build_data._untar(tmpdir, "test.tar.gz")
          assert os.path.exists(os.path.join(tmpdir, "test1.txt"))
          assert os.path.exists(os.path.join(tmpdir, "test2.txt"))
          with open(os.path.join(tmpdir, "test1.txt")) as f:
              assert f.read() == "Test1\n"
          with open(os.path.join(tmpdir, "test2.txt")) as f:
              assert f.read() == "Test2\n"
          assert not os.path.exists(zname)
  
imports: import os
  import pytest
  from parlai.core import build_data
  import unittest
  import unittest.mock
  import requests
  import parlai.utils.testing
  import multiprocessing
  from parlai.utils.io import PathManager
  from parlai.core.params import ParlaiParser
label_desc: Use image node_id 3 for calling the TestUnzip obj's underlying member method code with example usage: obj.test_untar() without return types