class_docstr: Mock downloading a tar.gz archive with a single file.
class_docstr_tok: ["Mock","downloading","a","tar.gz","archive","with","a","single","file","."]
code: def __init__(self, cache_root: str):
      super().__init__(
          url=...,
          name=...,
          relative_path="nations/train.txt",
          cache_root=cache_root,
      )
  
imports: import pathlib
  import unittest
  from io import BytesIO
  from urllib.request import urlopen
  from pykeen.datasets import Kinships, Nations, dataset_resolver
  from pykeen.datasets.base import PackedZipRemoteDataset, SingleTabbedDataset, TarFileRemoteDataset, TarFileSingleDataset, UnpackedRemoteDataset
  from pykeen.datasets.nations import NATIONS_TEST_PATH, NATIONS_TRAIN_PATH, NATIONS_VALIDATE_PATH
  from tests import cases, constants
label_desc: Use image node_id 1 to create a new MockTarFileSingleDataset object from inherited base classes: TarFileSingleDataset with example: obj = MockTarFileSingleDataset(cache_root)