class_docstr: Download manager test.
  
  During tests, the `tf.io.gfile` API is mocked. Instead, files I/O are tracked
  through `fs` (`tfds.testing.MockFs`).
  
  The downloader/extrator results are mocked with:
  
    dl_results: Dict[str, UrlInfo], mapping `url` -> `downloader.download(url)`
    dl_fnames: Dict[str, str], mapping `url` -> `filename`, if the name
      cannot be extracted from the url (e.g. `https://a.org/download?id=123`)
    extract_results: Dict[str, str], mapping `path` -> `extractor.extract()`
  
  To check whether url/path are actually downloaded vs cached reused:
  
    downloaded_urls: Track calls of `downloader.download`
    extracted_paths: Track calls of `extractor.extract`
class_docstr_tok: ["Download","manager","test",".","During","tests",",","the","`","tf.io.gfile","`","API","is","mocked",".","Instead",",","files","I\/O","are","tracked","through","`","fs","`","(","`","tfds.testing.MockFs","`",")",".","The","downloader\/extrator","results","are","mocked","with",":","dl_results",":","Dict","[","str",",","UrlInfo","]",",","mapping","`","url","`","-",">","`","downloader.download","(","url",")","`","dl_fnames",":","Dict","[","str",",","str","]",",","mapping","`","url","`","-",">","`","filename","`",",","if","the","name","can","not","be","extracted","from","the","url","(","e.g",".","`","https",":","\/\/a.org\/download","?","id=123","`",")","extract_results",":","Dict","[","str",",","str","]",",","mapping","`","path","`","-",">","`","extractor.extract","(",")","`","To","check","whether","url\/path","are","actually","downloaded","vs","cached","reused",":","downloaded_urls",":","Track","calls","of","`","downloader.download","`","extracted_paths",":","Track","calls","of","`","extractor.extract","`"]
code: def test_max_simultaneous_downloads(self, max_simultaneous_downloads):
      dl_manager = self._get_manager(
          max_simultaneous_downloads=max_simultaneous_downloads
      )
  
      self.assertEqual(
          max_simultaneous_downloads,
          dl_manager._downloader._executor._max_workers,
      )
  
imports: import collections
  import hashlib
  import json
  import os
  import pickle
  from unittest import mock
  from absl.testing import parameterized
  from etils import epath
  import promise
  import tensorflow
  from tensorflow_datasets import testing
  from tensorflow_datasets.core.download import checksums
  from tensorflow_datasets.core.download import download_manager
  from tensorflow_datasets.core.download import downloader
  from tensorflow_datasets.core.download import extractor
  from tensorflow_datasets.core.download import resource
  from tensorflow_datasets.core.utils import tree_utils
label_desc: Use image node_id 25 for calling the DownloadManagerTest obj's underlying member method code with example usage: obj.test_max_simultaneous_downloads(max_simultaneous_downloads) without return types