code: def test_ensure_file_defaults_to_DASK_CONFIG_directory(tmpdir):
      a = {"x": 1, "y": {"a": 1}}
      source = os.path.join(str(tmpdir), "source.yaml")
      with open(source, "w") as f:
          yaml.dump(a, f)
  
      destination = os.path.join(str(tmpdir), "dask")
      PATH = dask.config.PATH
      try:
          dask.config.PATH = destination
          ensure_file(source=source)
      finally:
          dask.config.PATH = PATH
  
      assert os.path.isdir(destination)
      [fn] = os.listdir(destination)
      assert os.path.split(fn)[1] == os.path.split(source)[1]
  
imports: from __future__ import annotations
  import os
  import site
  import stat
  import sys
  from collections import OrderedDict
  from contextlib import contextmanager
  import pytest
  import yaml
  import dask.config
  from dask.config import _get_paths, canonical_name, collect, collect_env, collect_yaml, config, deserialize, ensure_file, expand_environment_variables, get, merge, pop, refresh, rename, serialize, update, update_defaults
  from dask.utils import tmpfile
label_desc: Use image node_id 25 for calling a global function with example usage: test_ensure_file_defaults_to_DASK_CONFIG_directory(tmpdir) without return types