class_docstr: Test basic data downloading functionality.
class_docstr_tok: ["Test","basic","data","downloading","functionality","."]
docstr: Test retrieving a single file.
docstr_tok: ["Test","retrieving","a","single","file","."]
code: def test_retrieve(self):
      """Test retrieving a single file."""
      import satpy
      from satpy.aux_download import find_registerable_files, retrieve
  
      file_registry = {}
      with satpy.config.set(
          config_path=[self.tmpdir], data_dir=str(self.tmpdir)
      ), mock.patch("satpy.aux_download._FILE_REGISTRY", file_registry):
          comp_file = "composites/README.rst"
          found_files = find_registerable_files()
          assert comp_file in found_files
          assert not self.tmpdir.join(comp_file).exists()
          retrieve(comp_file)
          assert self.tmpdir.join(comp_file).exists()
  
imports: from unittest import mock
  import pytest
  import yaml
  from satpy.aux_download import DataDownloadMixin
  from satpy.modifiers import ModifierBase
label_desc: Use image node_id 4 for calling the TestDataDownload obj's underlying member method code with example usage: obj.test_retrieve() without return types