code: def test_concat_str() -> None:
      df = pl.DataFrame({"a": ["a", "b", "c"], "b": [1, 2, 3]})
  
      out = df.select([pl.concat_str(["a", "b"], separator="-")])
      assert out["a"].to_list() == ["a-1", "b-2", "c-3"]
  
imports: from __future__ import annotations
  from datetime import date, datetime
  from typing import TYPE_CHECKING
  import pytest
  import polars
  from polars.testing import assert_frame_equal, assert_series_equal
label_desc: Use image node_id 24 for calling a global function with example usage: test_concat_str() without return types