code: def test_metadata() -> None:
      df = pl.DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
      dfi = PolarsDataFrame(df)
      assert dfi.metadata == {}
  
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 3 for calling a global function with example usage: test_metadata() without return types