gh-137829: Fix shelve tests for backend compatibility

Lib/test/test_shelve.py

@@ -173,6 +173,8 @@ def test_custom_serializer_and_deserializer(self):
         def serializer(obj, protocol):
             if isinstance(obj, (bytes, bytearray, str)):
                 if protocol == 5:
+                    if isinstance(obj, bytearray):
+                        return bytes(obj)  # DBM backends expect bytes
                     return obj
                 return type(obj).__name__
             elif isinstance(obj, array.array):
@@ -222,22 +224,44 @@ def deserializer(data):
                         s["array_data"], array_data.tobytes().decode()
                     )
 
-    def test_custom_incomplete_serializer_and_deserializer(self):
-        dbm_sqlite3 = import_helper.import_module("dbm.sqlite3")
+    def test_custom_incomplete_serializer(self):
         os.mkdir(self.dirname)
         self.addCleanup(os_helper.rmtree, self.dirname)
 
-        with self.assertRaises(dbm_sqlite3.error):
-            def serializer(obj, protocol=None):
-                pass
+        def serializer(obj, protocol=None):
+            pass
 
-            def deserializer(data):
-                return data.decode("utf-8")
+        def deserializer(data):
+            return data.decode("utf-8")
+
+        # Since the serializer returns None, dbm.error is raised
+        # by dbm.sqlite3 and TypeError is raised by other backends.
+        with self.assertRaises((TypeError, dbm.error)):
+            with shelve.open(self.fn, serializer=serializer,
+                             deserializer=deserializer) as s:
+                s["foo"] = "bar"
+
+    def test_custom_invalid_serializer(self):
+        os.mkdir(self.dirname)
+        self.addCleanup(os_helper.rmtree, self.dirname)
 
+        def serializer(obj, protocol=None):
+            return ["value with invalid type"]
+
+        def deserializer(data):
+            return data.decode("utf-8")
+
+        # Since the serializer returns None, dbm.error is raised
+        # by dbm.sqlite3 and TypeError is raised by other backends.
+        with self.assertRaises((TypeError, dbm.error)):
             with shelve.open(self.fn, serializer=serializer,
                              deserializer=deserializer) as s:
                 s["foo"] = "bar"
 
+    def test_custom_incomplete_deserializer(self):
+        os.mkdir(self.dirname)
+        self.addCleanup(os_helper.rmtree, self.dirname)
+
         def serializer(obj, protocol=None):
             return type(obj).__name__.encode("utf-8")
 
@@ -352,7 +376,7 @@ def type_name_len(obj):
                     self.assertEqual(s["bytearray_data"], "bytearray")
                     self.assertEqual(s["array_data"], "array")
 
-    def test_custom_incomplete_serializer_and_deserializer_bsd_db_shelf(self):
+    def test_custom_incomplete_deserializer_bsd_db_shelf(self):
         berkeleydb = import_helper.import_module("berkeleydb")
         os.mkdir(self.dirname)
         self.addCleanup(os_helper.rmtree, self.dirname)
@@ -370,6 +394,11 @@ def deserializer(data):
             self.assertIsNone(s["foo"])
             self.assertNotEqual(s["foo"], "bar")
 
+    def test_custom_incomplete_serializer_bsd_db_shelf(self):
+        berkeleydb = import_helper.import_module("berkeleydb")
+        os.mkdir(self.dirname)
+        self.addCleanup(os_helper.rmtree, self.dirname)
+
         def serializer(obj, protocol=None):
             pass