code: def test_column_names() -> None:
      df = pl.DataFrame({"a": [1], "b": [2]})
      dfi = PolarsDataFrame(df)
      assert dfi.column_names() == ["a", "b"]
  
imports: from __future__ import annotations
  import pytest
  import polars
  from polars.interchange.dataframe import PolarsDataFrame
  from polars.interchange.protocol import CopyNotAllowedError
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 7 for calling a global function with example usage: test_column_names() without return types