code: def test_download(self, tmp_path):
      download_fn_was_called = False
  
      def download_fn(resource, root):
          nonlocal download_fn_was_called
          download_fn_was_called = True
  
          return self._make_file(
              root, content="_", name=resource.file_name
          )
  
      resource = self.DummyResource(
          file_name="file.txt",
          download_fn=download_fn,
      )
  
      resource.load(tmp_path)
  
      assert download_fn_was_called, "`download_fn()` was never called"
  
imports: import gzip
  import pathlib
  import sys
  import numpy
  import pytest
  import torch
  from datasets_utils import make_fake_flo_file, make_tar
  from torchdata.datapipes.iter import FileOpener, TarArchiveLoader
  from torchvision.datasets._optical_flow import _read_flo
  from torchvision.datasets.utils import _decompress
  from torchvision.prototype.datasets.utils import Dataset, GDriveResource, HttpResource, OnlineResource
  from torchvision.prototype.datasets.utils._internal import fromfile, read_flo
label_desc: Use image node_id 9 for calling the TestOnlineResource obj's underlying member method code with example usage: obj.test_download(tmp_path) and returns: self