code: def test_unique() -> None:
      ldf = pl.LazyFrame({"a": [1, 2, 2], "b": [3, 3, 3]})
  
      expected = pl.DataFrame({"a": [1, 2], "b": [3, 3]})
      assert_frame_equal(
          ldf.unique(maintain_order=True).collect(), expected
      )
  
      result = ldf.unique(subset="b", maintain_order=True).collect()
      expected = pl.DataFrame({"a": [1], "b": [3]})
      assert_frame_equal(result, expected)
  
      s0 = pl.Series("a", [1, 2, None, 2])
      # test if the null is included
      assert s0.unique().to_list() == [None, 1, 2]
  
file_path: polars/py-polars/tests/unit/operations/unique/test_unique.py
imports: from __future__ import annotations
  from datetime import date
  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_unique() without return types