TST: Add any_string_dtype parameterization to test (pandas-dev#44938)

Author: mroeschke

pandas/tests/strings/test_split_partition.py

@@ -434,10 +434,10 @@ def test_split_with_name_index():
         ],
     ],
 )
-def test_partition_series_more_than_one_char(method, exp):
+def test_partition_series_more_than_one_char(method, exp, any_string_dtype):
     # https://github.com/pandas-dev/pandas/issues/23558
     # more than one char
-    s = Series(["a__b__c", "c__d__e", np.nan, "f__g__h", None])
+    s = Series(["a__b__c", "c__d__e", np.nan, "f__g__h", None], dtype=any_string_dtype)
     result = getattr(s.str, method)("__", expand=False)
     expected = Series(exp)
     tm.assert_series_equal(result, expected)