code: def test_spilt_join_roundtrip(any_string_dtype):
      ser = Series(
          ["a_b_c", "c_d_e", np.nan, "f_g_h"], dtype=any_string_dtype
      )
      result = ser.str.split("_").str.join("_")
      expected = ser.astype(object)
      tm.assert_series_equal(result, expected)
  
imports: from datetime import datetime, timedelta
  import numpy
  import pytest
  from pandas import DataFrame, Index, MultiIndex, Series
  import pandas._testing
  from pandas.core.strings.accessor import StringMethods
  from pandas.tests.strings import object_pyarrow_numpy
label_desc: Use image node_id 12 for calling a global function with example usage: test_spilt_join_roundtrip(any_string_dtype) without return types