fix string arith tests

Author: jorisvandenbossche

pandas/tests/arrays/string_/test_string.py

@@ -53,6 +53,12 @@ def cls(dtype):
 ]
 
 
+def string_dtype_highest_priority(dtype1, dtype2):
+    h1 = DTYPE_HIERARCHY.index(dtype1)
+    h2 = DTYPE_HIERARCHY.index(dtype2)
+    return DTYPE_HIERARCHY[max(h1, h2)]
+
+
 def test_dtype_constructor():
     pytest.importorskip("pyarrow")
 
@@ -347,9 +353,7 @@ def test_comparison_methods_array(comparison_op, dtype, dtype2):
         tm.assert_numpy_array_equal(result, expected)
 
     else:
-        h1 = DTYPE_HIERARCHY.index(dtype)
-        h2 = DTYPE_HIERARCHY.index(dtype2)
-        max_dtype = DTYPE_HIERARCHY[max(h1, h2)]
+        max_dtype = string_dtype_highest_priority(dtype, dtype2)
         if max_dtype.storage == "python":
             expected_dtype = "boolean"
         else:

pandas/tests/extension/test_string.py

@@ -22,15 +22,14 @@
 import numpy as np
 import pytest
 
-from pandas.compat import HAS_PYARROW
-
 from pandas.core.dtypes.base import StorageExtensionDtype
 
 import pandas as pd
 import pandas._testing as tm
 from pandas.api.types import is_string_dtype
 from pandas.core.arrays import ArrowStringArray
 from pandas.core.arrays.string_ import StringDtype
+from pandas.tests.arrays.string_.test_string import string_dtype_highest_priority
 from pandas.tests.extension import base
 
 
@@ -202,10 +201,13 @@ def _cast_pointwise_result(self, op_name: str, obj, other, pointwise_result):
         dtype = cast(StringDtype, tm.get_dtype(obj))
         if op_name in ["__add__", "__radd__"]:
             cast_to = dtype
+            dtype_other = tm.get_dtype(other) if not isinstance(other, str) else None
+            if isinstance(dtype_other, StringDtype):
+                cast_to = string_dtype_highest_priority(dtype, dtype_other)
         elif dtype.na_value is np.nan:
             cast_to = np.bool_  # type: ignore[assignment]
         elif dtype.storage == "pyarrow":
-            cast_to = "boolean[pyarrow]"  # type: ignore[assignment]
+            cast_to = "bool[pyarrow]"  # type: ignore[assignment]
         else:
             cast_to = "boolean"  # type: ignore[assignment]
         return pointwise_result.astype(cast_to)
@@ -236,9 +238,7 @@ def test_arith_series_with_array(
         if (
             using_infer_string
             and all_arithmetic_operators == "__radd__"
-            and (
-                (dtype.na_value is pd.NA) or (dtype.storage == "python" and HAS_PYARROW)
-            )
+            and dtype.na_value is pd.NA
         ):
             mark = pytest.mark.xfail(
                 reason="The pointwise operation result will be inferred to "