code: def test_get_validity_buffer() -> None:
      s = pl.Series(["a", None, "b"])
      col = PolarsColumn(s)
  
      validity = col._get_validity_buffer()
  
      assert validity is not None
  
      result_buffer, result_dtype = validity
      expected = pl.Series([True, False, True])
      assert_series_equal(result_buffer._data, expected)
      assert result_dtype == (DtypeKind.BOOL, 1, "b", "=")
  
imports: from __future__ import annotations
  from datetime import datetime
  from typing import TYPE_CHECKING
  import pytest
  import polars
  from polars.interchange.column import PolarsColumn
  from polars.interchange.protocol import ColumnNullType, CopyNotAllowedError, DtypeKind
  from polars.testing import assert_series_equal
label_desc: Use image node_id 23 for calling a global function with example usage: test_get_validity_buffer() without return types