code: def test_is_selector() -> None:
      assert is_selector(cs.numeric())
      assert is_selector(cs.by_dtype(pl.UInt32) | pl.col("xyz"))
      assert not is_selector(pl.col("cde"))
      assert not is_selector(None)
  
imports: from typing import Any
  import pytest
  import polars
  import polars.selectors
  from polars.selectors import expand_selector, is_selector
  from polars.testing import assert_frame_equal
label_desc: Use image node_id 27 for calling a global function with example usage: test_is_selector() without return types