code: def test_replace_regex(any_string_dtype):
      # https://github.com/pandas-dev/pandas/pull/24809
      s = Series(["a", "b", "ac", np.nan, ""], dtype=any_string_dtype)
      result = s.str.replace("^.$", "a", regex=True)
      expected = Series(
          ["a", "a", "ac", np.nan, ""], dtype=any_string_dtype
      )
      tm.assert_series_equal(result, expected)
  
imports: from datetime import datetime
  import re
  import numpy
  import pytest
  from pandas.errors import PerformanceWarning
  import pandas.util._test_decorators
  import pandas
  from pandas import Series, _testing
  from pandas.tests.strings import _convert_na_value, object_pyarrow_numpy
label_desc: Use image node_id 30 for calling a global function with example usage: test_replace_regex(any_string_dtype) without return types