code: def test_group_by_empty() -> None:
      df = pl.DataFrame({"a": [1, 1, 2]})
      result = df.group_by("a").agg()
      expected = pl.DataFrame({"a": [1, 2]})
      assert_frame_equal(result, expected, check_row_order=False)
  
imports: from __future__ import annotations
  from collections import OrderedDict
  from datetime import datetime, timedelta
  from typing import Any
  import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 6 for calling a global function with example usage: test_group_by_empty() without return types