code: def test_auto_compression():
      """Test that the 'auto' compression algorithm is lz4 -> snappy -> None.
      If neither is installed, test that we don't fall back to the very slow zlib.
      """
      with dask.config.set({"test123": "auto"}):
          try:
              import lz4  # noqa: F401
  
              assert get_compression_settings("test123") == "lz4"
              return
          except ImportError:
              pass
  
          try:
              import snappy  # noqa: F401
  
              assert get_compression_settings("test123") == "snappy"
          except ImportError:
              assert get_compression_settings("test123") is None
  
imports: from __future__ import annotations
  import threading
  import zlib
  from concurrent.futures import ThreadPoolExecutor
  import pytest
  import dask.config
  from distributed import Worker, wait
  from distributed.compatibility import LINUX
  from distributed.protocol import dumps, loads, maybe_compress, msgpack, to_serialize
  from distributed.protocol.compression import Compression, compressions, get_compression_settings
  from distributed.utils import nbytes
  from distributed.utils_test import gen_cluster
label_desc: Use image node_id 4 for calling a global function with example usage: test_auto_compression() without return types