diff --git a/Lib/pickle.py b/Lib/pickle.py
index beaefae04..7b9518586 100644
--- a/Lib/pickle.py
+++ b/Lib/pickle.py
@@ -904,17 +904,11 @@ class _Pickler:
                     # Write data in-band
                     # XXX The C implementation avoids a copy here
                     buf = m.tobytes()
-                    in_memo = id(buf) in self.memo
                     if m.readonly:
-                        if in_memo:
-                            self._save_bytes_no_memo(buf)
-                        else:
-                            self.save_bytes(buf)
+                        self._save_bytes_no_memo(buf)
                     else:
-                        if in_memo:
-                            self._save_bytearray_no_memo(buf)
-                        else:
-                            self.save_bytearray(buf)
+                        self._save_bytearray_no_memo(buf)
+                    self.memoize(obj)
                 else:
                     # Write data out-of-band
                     self.write(NEXT_BUFFER)
diff --git a/Lib/test/picklecommon.py b/Lib/test/picklecommon.py
new file mode 100644
index 000000000..4c19b6c42
--- /dev/null
+++ b/Lib/test/picklecommon.py
@@ -0,0 +1,390 @@
+# Classes used for pickle testing.
+# They are moved to separate file, so they can be loaded
+# in other Python version for test_xpickle.
+
+import sys
+
+class C:
+    def __eq__(self, other):
+        return self.__dict__ == other.__dict__
+
+# For test_load_classic_instance
+class D(C):
+    def __init__(self, arg):
+        pass
+
+class E(C):
+    def __getinitargs__(self):
+        return ()
+
+import __main__
+__main__.C = C
+C.__module__ = "__main__"
+__main__.D = D
+D.__module__ = "__main__"
+__main__.E = E
+E.__module__ = "__main__"
+
+# Simple mutable object.
+class Object(object):
+    pass
+
+# Hashable immutable key object containing unheshable mutable data.
+class K:
+    def __init__(self, value):
+        self.value = value
+
+    def __reduce__(self):
+        # Shouldn't support the recursion itself
+        return K, (self.value,)
+
+class WithSlots(object):
+    __slots__ = ('a', 'b')
+
+class WithSlotsSubclass(WithSlots):
+    __slots__ = ('c',)
+
+class WithSlotsAndDict(object):
+    __slots__ = ('a', '__dict__')
+
+class WithPrivateAttrs(object):
+    def __init__(self, a):
+        self.__private = a
+    def get(self):
+        return self.__private
+
+class WithPrivateAttrsSubclass(WithPrivateAttrs):
+    def __init__(self, a, b):
+        super().__init__(a)
+        self.__private = b
+    def get2(self):
+        return self.__private
+
+class WithPrivateSlots(object):
+    __slots__ = ('__private',)
+    def __init__(self, a):
+        self.__private = a
+    def get(self):
+        return self.__private
+
+class WithPrivateSlotsSubclass(WithPrivateSlots):
+    __slots__ = ('__private',)
+    def __init__(self, a, b):
+        super().__init__(a)
+        self.__private = b
+    def get2(self):
+        return self.__private
+
+# For test_misc
+class myint(int):
+    def __init__(self, x):
+        self.str = str(x)
+
+# For test_misc and test_getinitargs
+class initarg(C):
+
+    def __init__(self, a, b):
+        self.a = a
+        self.b = b
+
+    def __getinitargs__(self):
+        return self.a, self.b
+
+# For test_metaclass
+class metaclass(type):
+    pass
+
+if sys.version_info >= (3,):
+    # Syntax not compatible with Python 2
+    exec('''
+class use_metaclass(object, metaclass=metaclass):
+    pass
+''')
+else:
+    class use_metaclass(object):
+        __metaclass__ = metaclass
+
+
+# Test classes for reduce_ex
+
+class R:
+    def __init__(self, reduce=None):
+        self.reduce = reduce
+    def __reduce__(self, proto):
+        return self.reduce
+
+class REX:
+    def __init__(self, reduce_ex=None):
+        self.reduce_ex = reduce_ex
+    def __reduce_ex__(self, proto):
+        return self.reduce_ex
+
+class REX_one(object):
+    """No __reduce_ex__ here, but inheriting it from object"""
+    _reduce_called = 0
+    def __reduce__(self):
+        self._reduce_called = 1
+        return REX_one, ()
+
+class REX_two(object):
+    """No __reduce__ here, but inheriting it from object"""
+    _proto = None
+    def __reduce_ex__(self, proto):
+        self._proto = proto
+        return REX_two, ()
+
+class REX_three(object):
+    _proto = None
+    def __reduce_ex__(self, proto):
+        self._proto = proto
+        return REX_two, ()
+    def __reduce__(self):
+        raise AssertionError("This __reduce__ shouldn't be called")
+
+class REX_four(object):
+    """Calling base class method should succeed"""
+    _proto = None
+    def __reduce_ex__(self, proto):
+        self._proto = proto
+        return object.__reduce_ex__(self, proto)
+
+class REX_five(object):
+    """This one used to fail with infinite recursion"""
+    _reduce_called = 0
+    def __reduce__(self):
+        self._reduce_called = 1
+        return object.__reduce__(self)
+
+class REX_six(object):
+    """This class is used to check the 4th argument (list iterator) of
+    the reduce protocol.
+    """
+    def __init__(self, items=None):
+        self.items = items if items is not None else []
+    def __eq__(self, other):
+        return type(self) is type(other) and self.items == other.items
+    def append(self, item):
+        self.items.append(item)
+    def __reduce__(self):
+        return type(self), (), None, iter(self.items), None
+
+class REX_seven(object):
+    """This class is used to check the 5th argument (dict iterator) of
+    the reduce protocol.
+    """
+    def __init__(self, table=None):
+        self.table = table if table is not None else {}
+    def __eq__(self, other):
+        return type(self) is type(other) and self.table == other.table
+    def __setitem__(self, key, value):
+        self.table[key] = value
+    def __reduce__(self):
+        return type(self), (), None, None, iter(self.table.items())
+
+class REX_state(object):
+    """This class is used to check the 3th argument (state) of
+    the reduce protocol.
+    """
+    def __init__(self, state=None):
+        self.state = state
+    def __eq__(self, other):
+        return type(self) is type(other) and self.state == other.state
+    def __setstate__(self, state):
+        self.state = state
+    def __reduce__(self):
+        return type(self), (), self.state
+
+# For test_reduce_ex_None
+class REX_None:
+    """ Setting __reduce_ex__ to None should fail """
+    __reduce_ex__ = None
+
+# For test_reduce_None
+class R_None:
+    """ Setting __reduce__ to None should fail """
+    __reduce__ = None
+
+# For test_pickle_setstate_None
+class C_None_setstate:
+    """  Setting __setstate__ to None should fail """
+    def __getstate__(self):
+        return 1
+
+    __setstate__ = None
+
+
+# Test classes for newobj
+
+# For test_newobj_generic and test_newobj_proxies
+
+class MyInt(int):
+    sample = 1
+
+if sys.version_info >= (3,):
+    class MyLong(int):
+        sample = 1
+else:
+    class MyLong(long):
+        sample = long(1)
+
+class MyFloat(float):
+    sample = 1.0
+
+class MyComplex(complex):
+    sample = 1.0 + 0.0j
+
+class MyStr(str):
+    sample = "hello"
+
+if sys.version_info >= (3,):
+    class MyUnicode(str):
+        sample = "hello \u1234"
+else:
+    class MyUnicode(unicode):
+        sample = unicode(r"hello \u1234", "raw-unicode-escape")
+
+class MyTuple(tuple):
+    sample = (1, 2, 3)
+
+class MyList(list):
+    sample = [1, 2, 3]
+
+class MyDict(dict):
+    sample = {"a": 1, "b": 2}
+
+class MySet(set):
+    sample = {"a", "b"}
+
+class MyFrozenSet(frozenset):
+    sample = frozenset({"a", "b"})
+
+myclasses = [MyInt, MyLong, MyFloat,
+             MyComplex,
+             MyStr, MyUnicode,
+             MyTuple, MyList, MyDict, MySet, MyFrozenSet]
+
+# For test_newobj_overridden_new
+class MyIntWithNew(int):
+    def __new__(cls, value):
+        raise AssertionError
+
+class MyIntWithNew2(MyIntWithNew):
+    __new__ = int.__new__
+
+
+# For test_newobj_list_slots
+class SlotList(MyList):
+    __slots__ = ["foo"]
+
+# Ruff "redefined while unused" false positive here due to `global` variables
+# being assigned (and then restored) from within test methods earlier in the file
+class SimpleNewObj(int):  # noqa: F811
+    def __init__(self, *args, **kwargs):
+        # raise an error, to make sure this isn't called
+        raise TypeError("SimpleNewObj.__init__() didn't expect to get called")
+    def __eq__(self, other):
+        return int(self) == int(other) and self.__dict__ == other.__dict__
+
+class ComplexNewObj(SimpleNewObj):
+    def __getnewargs__(self):
+        return ('%X' % self, 16)
+
+class ComplexNewObjEx(SimpleNewObj):
+    def __getnewargs_ex__(self):
+        return ('%X' % self,), {'base': 16}
+
+
+class ZeroCopyBytes(bytes):
+    readonly = True
+    c_contiguous = True
+    f_contiguous = True
+    zero_copy_reconstruct = True
+
+    def __reduce_ex__(self, protocol):
+        if protocol >= 5:
+            import pickle
+            return type(self)._reconstruct, (pickle.PickleBuffer(self),), None
+        else:
+            return type(self)._reconstruct, (bytes(self),)
+
+    def __repr__(self):
+        return "{}({!r})".format(self.__class__.__name__, bytes(self))
+
+    __str__ = __repr__
+
+    @classmethod
+    def _reconstruct(cls, obj):
+        with memoryview(obj) as m:
+            obj = m.obj
+            if type(obj) is cls:
+                # Zero-copy
+                return obj
+            else:
+                return cls(obj)
+
+
+class ZeroCopyBytearray(bytearray):
+    readonly = False
+    c_contiguous = True
+    f_contiguous = True
+    zero_copy_reconstruct = True
+
+    def __reduce_ex__(self, protocol):
+        if protocol >= 5:
+            import pickle
+            return type(self)._reconstruct, (pickle.PickleBuffer(self),), None
+        else:
+            return type(self)._reconstruct, (bytes(self),)
+
+    def __repr__(self):
+        return "{}({!r})".format(self.__class__.__name__, bytes(self))
+
+    __str__ = __repr__
+
+    @classmethod
+    def _reconstruct(cls, obj):
+        with memoryview(obj) as m:
+            obj = m.obj
+            if type(obj) is cls:
+                # Zero-copy
+                return obj
+            else:
+                return cls(obj)
+
+
+# For test_nested_names
+class Nested:
+    class A:
+        class B:
+            class C:
+                pass
+
+# For test_py_methods
+class PyMethodsTest:
+    @staticmethod
+    def cheese():
+        return "cheese"
+    @classmethod
+    def wine(cls):
+        assert cls is PyMethodsTest
+        return "wine"
+    def biscuits(self):
+        assert isinstance(self, PyMethodsTest)
+        return "biscuits"
+    class Nested:
+        "Nested class"
+        @staticmethod
+        def ketchup():
+            return "ketchup"
+        @classmethod
+        def maple(cls):
+            assert cls is PyMethodsTest.Nested
+            return "maple"
+        def pie(self):
+            assert isinstance(self, PyMethodsTest.Nested)
+            return "pie"
+
+# For test_c_methods
+class Subclass(tuple):
+    class Nested(str):
+        pass
diff --git a/Lib/test/pickletester.py b/Lib/test/pickletester.py
index 9a3a26a84..7c81ba8db 100644
--- a/Lib/test/pickletester.py
+++ b/Lib/test/pickletester.py
@@ -15,6 +15,7 @@ import threading
 import types
 import unittest
 import weakref
+import __main__
 from textwrap import dedent
 from http.cookies import SimpleCookie
 
@@ -26,13 +27,15 @@ except ImportError:
 from test import support
 from test.support import os_helper
 from test.support import (
-    TestFailed, run_with_locales, no_tracing,
+    run_with_locales, no_tracing,
     _2G, _4G, bigmemtest
     )
 from test.support.import_helper import forget
 from test.support.os_helper import TESTFN
 from test.support import threading_helper
 from test.support.warnings_helper import save_restore_warnings_filters
+from test import picklecommon
+from test.picklecommon import *
 
 from pickle import bytes_types
 
@@ -54,6 +57,8 @@ requires_32b = unittest.skipUnless(sys.maxsize < 2**32,
 # kind of outer loop.
 protocols = range(pickle.HIGHEST_PROTOCOL + 1)
 
+FAST_NESTING_LIMIT = 50
+
 
 # Return True if opcode code appears in the pickle, else False.
 def opcode_in_pickle(code, pickle):
@@ -132,58 +137,6 @@ class ExtensionSaver:
         if pair is not None:
             copyreg.add_extension(pair[0], pair[1], code)
 
-class C:
-    def __eq__(self, other):
-        return self.__dict__ == other.__dict__
-
-class D(C):
-    def __init__(self, arg):
-        pass
-
-class E(C):
-    def __getinitargs__(self):
-        return ()
-
-import __main__
-__main__.C = C
-C.__module__ = "__main__"
-__main__.D = D
-D.__module__ = "__main__"
-__main__.E = E
-E.__module__ = "__main__"
-
-# Simple mutable object.
-class Object:
-    pass
-
-# Hashable immutable key object containing unheshable mutable data.
-class K:
-    def __init__(self, value):
-        self.value = value
-
-    def __reduce__(self):
-        # Shouldn't support the recursion itself
-        return K, (self.value,)
-
-class myint(int):
-    def __init__(self, x):
-        self.str = str(x)
-
-class initarg(C):
-
-    def __init__(self, a, b):
-        self.a = a
-        self.b = b
-
-    def __getinitargs__(self):
-        return self.a, self.b
-
-class metaclass(type):
-    pass
-
-class use_metaclass(object, metaclass=metaclass):
-    pass
-
 class pickling_metaclass(type):
     def __eq__(self, other):
         return (type(self) == type(other) and
@@ -198,62 +151,6 @@ def create_dynamic_class(name, bases):
     return result
 
 
-class ZeroCopyBytes(bytes):
-    readonly = True
-    c_contiguous = True
-    f_contiguous = True
-    zero_copy_reconstruct = True
-
-    def __reduce_ex__(self, protocol):
-        if protocol >= 5:
-            return type(self)._reconstruct, (pickle.PickleBuffer(self),), None
-        else:
-            return type(self)._reconstruct, (bytes(self),)
-
-    def __repr__(self):
-        return "{}({!r})".format(self.__class__.__name__, bytes(self))
-
-    __str__ = __repr__
-
-    @classmethod
-    def _reconstruct(cls, obj):
-        with memoryview(obj) as m:
-            obj = m.obj
-            if type(obj) is cls:
-                # Zero-copy
-                return obj
-            else:
-                return cls(obj)
-
-
-class ZeroCopyBytearray(bytearray):
-    readonly = False
-    c_contiguous = True
-    f_contiguous = True
-    zero_copy_reconstruct = True
-
-    def __reduce_ex__(self, protocol):
-        if protocol >= 5:
-            return type(self)._reconstruct, (pickle.PickleBuffer(self),), None
-        else:
-            return type(self)._reconstruct, (bytes(self),)
-
-    def __repr__(self):
-        return "{}({!r})".format(self.__class__.__name__, bytes(self))
-
-    __str__ = __repr__
-
-    @classmethod
-    def _reconstruct(cls, obj):
-        with memoryview(obj) as m:
-            obj = m.obj
-            if type(obj) is cls:
-                # Zero-copy
-                return obj
-            else:
-                return cls(obj)
-
-
 if _testbuffer is not None:
 
     class PicklableNDArray:
@@ -298,9 +195,10 @@ if _testbuffer is not None:
             return not (self == other)
 
         def __repr__(self):
-            return (f"{type(self)}(shape={self.array.shape},"
-                    f"strides={self.array.strides}, "
-                    f"bytes={self.array.tobytes()})")
+            return ("{name}(shape={array.shape},"
+                    "strides={array.strides}, "
+                    "bytes={array.tobytes()})").format(
+                    name=type(self).__name__, array=self.array.shape)
 
         def __reduce_ex__(self, protocol):
             if not self.array.contiguous:
@@ -1359,9 +1257,9 @@ class AbstractUnpickleTests:
                     self.loads(b'\x82\x01.')
         check(None, ValueError)
         check((), ValueError)
-        check((__name__,), (TypeError, ValueError))
-        check((__name__, "MyList", "x"), (TypeError, ValueError))
-        check((__name__, None), (TypeError, ValueError))
+        check((MyList.__module__,), (TypeError, ValueError))
+        check((MyList.__module__, "MyList", "x"), (TypeError, ValueError))
+        check((MyList.__module__, None), (TypeError, ValueError))
         check((None, "MyList"), (TypeError, ValueError))
 
     def test_bad_reduce(self):
@@ -1675,7 +1573,7 @@ class AbstractPicklingErrorTests:
                 self.assertEqual(str(cm.exception),
                     '__reduce__ must return a string or tuple, not list')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         obj = REX((print,))
         for proto in protocols:
@@ -1685,7 +1583,7 @@ class AbstractPicklingErrorTests:
                 self.assertEqual(str(cm.exception),
                     'tuple returned by __reduce__ must contain 2 through 6 elements')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         obj = REX((print, (), None, None, None, None, None))
         for proto in protocols:
@@ -1695,7 +1593,7 @@ class AbstractPicklingErrorTests:
                 self.assertEqual(str(cm.exception),
                     'tuple returned by __reduce__ must contain 2 through 6 elements')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_bad_reconstructor(self):
         obj = REX((42, ()))
@@ -1707,7 +1605,7 @@ class AbstractPicklingErrorTests:
                     'first item of the tuple returned by __reduce__ '
                     'must be callable, not int')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_reconstructor(self):
         obj = REX((UnpickleableCallable(), ()))
@@ -1716,8 +1614,8 @@ class AbstractPicklingErrorTests:
                 with self.assertRaises(CustomError) as cm:
                     self.dumps(obj, proto)
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX reconstructor',
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX reconstructor',
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_bad_reconstructor_args(self):
         obj = REX((print, []))
@@ -1729,7 +1627,7 @@ class AbstractPicklingErrorTests:
                     'second item of the tuple returned by __reduce__ '
                     'must be a tuple, not list')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_reconstructor_args(self):
         obj = REX((print, (1, 2, UNPICKLEABLE)))
@@ -1739,8 +1637,8 @@ class AbstractPicklingErrorTests:
                     self.dumps(obj, proto)
                 self.assertEqual(cm.exception.__notes__, [
                     'when serializing tuple item 2',
-                    'when serializing test.pickletester.REX reconstructor arguments',
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX reconstructor arguments',
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_bad_newobj_args(self):
         obj = REX((copyreg.__newobj__, ()))
@@ -1752,7 +1650,7 @@ class AbstractPicklingErrorTests:
                     'tuple index out of range',
                     '__newobj__ expected at least 1 argument, got 0'})
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         obj = REX((copyreg.__newobj__, [REX]))
         for proto in protocols[2:]:
@@ -1763,7 +1661,7 @@ class AbstractPicklingErrorTests:
                     'second item of the tuple returned by __reduce__ '
                     'must be a tuple, not list')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_bad_newobj_class(self):
         obj = REX((copyreg.__newobj__, (NoNew(),)))
@@ -1773,9 +1671,9 @@ class AbstractPicklingErrorTests:
                     self.dumps(obj, proto)
                 self.assertIn(str(cm.exception), {
                     'first argument to __newobj__() has no __new__',
-                    f'first argument to __newobj__() must be a class, not {__name__}.NoNew'})
+                    f'first argument to __newobj__() must be a class, not {NoNew.__module__}.NoNew'})
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_wrong_newobj_class(self):
         obj = REX((copyreg.__newobj__, (str,)))
@@ -1786,7 +1684,7 @@ class AbstractPicklingErrorTests:
                 self.assertEqual(str(cm.exception),
                     f'first argument to __newobj__() must be {REX!r}, not {str!r}')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_newobj_class(self):
         class LocalREX(REX): pass
@@ -1814,13 +1712,13 @@ class AbstractPicklingErrorTests:
                 if proto >= 2:
                     self.assertEqual(cm.exception.__notes__, [
                         'when serializing tuple item 2',
-                        'when serializing test.pickletester.REX __new__ arguments',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX __new__ arguments',
+                        f'when serializing {REX.__module__}.REX object'])
                 else:
                     self.assertEqual(cm.exception.__notes__, [
                         'when serializing tuple item 3',
-                        'when serializing test.pickletester.REX reconstructor arguments',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX reconstructor arguments',
+                        f'when serializing {REX.__module__}.REX object'])
 
     def test_bad_newobj_ex_args(self):
         obj = REX((copyreg.__newobj_ex__, ()))
@@ -1832,7 +1730,7 @@ class AbstractPicklingErrorTests:
                     'not enough values to unpack (expected 3, got 0)',
                     '__newobj_ex__ expected 3 arguments, got 0'})
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         obj = REX((copyreg.__newobj_ex__, 42))
         for proto in protocols[2:]:
@@ -1843,7 +1741,7 @@ class AbstractPicklingErrorTests:
                     'second item of the tuple returned by __reduce__ '
                     'must be a tuple, not int')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         obj = REX((copyreg.__newobj_ex__, (REX, 42, {})))
         if self.pickler is pickle._Pickler:
@@ -1854,7 +1752,7 @@ class AbstractPicklingErrorTests:
                     self.assertEqual(str(cm.exception),
                         'Value after * must be an iterable, not int')
                     self.assertEqual(cm.exception.__notes__, [
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX object'])
         else:
             for proto in protocols[2:]:
                 with self.subTest(proto=proto):
@@ -1863,7 +1761,7 @@ class AbstractPicklingErrorTests:
                     self.assertEqual(str(cm.exception),
                         'second argument to __newobj_ex__() must be a tuple, not int')
                     self.assertEqual(cm.exception.__notes__, [
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX object'])
 
         obj = REX((copyreg.__newobj_ex__, (REX, (), [])))
         if self.pickler is pickle._Pickler:
@@ -1874,7 +1772,7 @@ class AbstractPicklingErrorTests:
                     self.assertEqual(str(cm.exception),
                         'functools.partial() argument after ** must be a mapping, not list')
                     self.assertEqual(cm.exception.__notes__, [
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX object'])
         else:
             for proto in protocols[2:]:
                 with self.subTest(proto=proto):
@@ -1883,7 +1781,7 @@ class AbstractPicklingErrorTests:
                     self.assertEqual(str(cm.exception),
                         'third argument to __newobj_ex__() must be a dict, not list')
                     self.assertEqual(cm.exception.__notes__, [
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX object'])
 
     def test_bad_newobj_ex__class(self):
         obj = REX((copyreg.__newobj_ex__, (NoNew(), (), {})))
@@ -1893,9 +1791,9 @@ class AbstractPicklingErrorTests:
                     self.dumps(obj, proto)
                 self.assertIn(str(cm.exception), {
                     'first argument to __newobj_ex__() has no __new__',
-                    f'first argument to __newobj_ex__() must be a class, not {__name__}.NoNew'})
+                    f'first argument to __newobj_ex__() must be a class, not {NoNew.__module__}.NoNew'})
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_wrong_newobj_ex_class(self):
         if self.pickler is not pickle._Pickler:
@@ -1908,7 +1806,7 @@ class AbstractPicklingErrorTests:
                 self.assertEqual(str(cm.exception),
                     f'first argument to __newobj_ex__() must be {REX}, not {str}')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_newobj_ex_class(self):
         class LocalREX(REX): pass
@@ -1944,22 +1842,22 @@ class AbstractPicklingErrorTests:
                 if proto >= 4:
                     self.assertEqual(cm.exception.__notes__, [
                         'when serializing tuple item 2',
-                        'when serializing test.pickletester.REX __new__ arguments',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX __new__ arguments',
+                        f'when serializing {REX.__module__}.REX object'])
                 elif proto >= 2:
                     self.assertEqual(cm.exception.__notes__, [
                         'when serializing tuple item 3',
                         'when serializing tuple item 1',
                         'when serializing functools.partial state',
                         'when serializing functools.partial object',
-                        'when serializing test.pickletester.REX reconstructor',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX reconstructor',
+                        f'when serializing {REX.__module__}.REX object'])
                 else:
                     self.assertEqual(cm.exception.__notes__, [
                         'when serializing tuple item 2',
                         'when serializing tuple item 1',
-                        'when serializing test.pickletester.REX reconstructor arguments',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX reconstructor arguments',
+                        f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_newobj_ex_kwargs(self):
         obj = REX((copyreg.__newobj_ex__, (REX, (), {'a': UNPICKLEABLE})))
@@ -1970,22 +1868,22 @@ class AbstractPicklingErrorTests:
                 if proto >= 4:
                     self.assertEqual(cm.exception.__notes__, [
                         "when serializing dict item 'a'",
-                        'when serializing test.pickletester.REX __new__ arguments',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX __new__ arguments',
+                        f'when serializing {REX.__module__}.REX object'])
                 elif proto >= 2:
                     self.assertEqual(cm.exception.__notes__, [
                         "when serializing dict item 'a'",
                         'when serializing tuple item 2',
                         'when serializing functools.partial state',
                         'when serializing functools.partial object',
-                        'when serializing test.pickletester.REX reconstructor',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX reconstructor',
+                        f'when serializing {REX.__module__}.REX object'])
                 else:
                     self.assertEqual(cm.exception.__notes__, [
                         "when serializing dict item 'a'",
                         'when serializing tuple item 2',
-                        'when serializing test.pickletester.REX reconstructor arguments',
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX reconstructor arguments',
+                        f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_state(self):
         obj = REX_state(UNPICKLEABLE)
@@ -1994,8 +1892,8 @@ class AbstractPicklingErrorTests:
                 with self.assertRaises(CustomError) as cm:
                     self.dumps(obj, proto)
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX_state state',
-                    'when serializing test.pickletester.REX_state object'])
+                    f'when serializing {REX_state.__module__}.REX_state state',
+                    f'when serializing {REX_state.__module__}.REX_state object'])
 
     def test_bad_state_setter(self):
         if self.pickler is pickle._Pickler:
@@ -2009,7 +1907,7 @@ class AbstractPicklingErrorTests:
                     'sixth item of the tuple returned by __reduce__ '
                     'must be callable, not int')
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_state_setter(self):
         obj = REX((print, (), 'state', None, None, UnpickleableCallable()))
@@ -2018,8 +1916,8 @@ class AbstractPicklingErrorTests:
                 with self.assertRaises(CustomError) as cm:
                     self.dumps(obj, proto)
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX state setter',
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX state setter',
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_state_with_state_setter(self):
         obj = REX((print, (), UNPICKLEABLE, None, None, print))
@@ -2028,8 +1926,8 @@ class AbstractPicklingErrorTests:
                 with self.assertRaises(CustomError) as cm:
                     self.dumps(obj, proto)
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX state',
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX state',
+                    f'when serializing {REX.__module__}.REX object'])
 
     def test_bad_object_list_items(self):
         # Issue4176: crash when 4th and 5th items of __reduce__()
@@ -2044,7 +1942,7 @@ class AbstractPicklingErrorTests:
                     'fourth item of the tuple returned by __reduce__ '
                     'must be an iterator, not int'})
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         if self.pickler is not pickle._Pickler:
             # Python implementation is less strict and also accepts iterables.
@@ -2057,7 +1955,7 @@ class AbstractPicklingErrorTests:
                         'fourth item of the tuple returned by __reduce__ '
                         'must be an iterator, not int')
                     self.assertEqual(cm.exception.__notes__, [
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_object_list_items(self):
         obj = REX_six([1, 2, UNPICKLEABLE])
@@ -2066,8 +1964,8 @@ class AbstractPicklingErrorTests:
                 with self.assertRaises(CustomError) as cm:
                     self.dumps(obj, proto)
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX_six item 2',
-                    'when serializing test.pickletester.REX_six object'])
+                    f'when serializing {REX_six.__module__}.REX_six item 2',
+                    f'when serializing {REX_six.__module__}.REX_six object'])
 
     def test_bad_object_dict_items(self):
         # Issue4176: crash when 4th and 5th items of __reduce__()
@@ -2082,7 +1980,7 @@ class AbstractPicklingErrorTests:
                     'fifth item of the tuple returned by __reduce__ '
                     'must be an iterator, not int'})
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         for proto in protocols:
             obj = REX((dict, (), None, None, iter([('a',)])))
@@ -2093,7 +1991,7 @@ class AbstractPicklingErrorTests:
                     'not enough values to unpack (expected 2, got 1)',
                     'dict items iterator must return 2-tuples'})
                 self.assertEqual(cm.exception.__notes__, [
-                    'when serializing test.pickletester.REX object'])
+                    f'when serializing {REX.__module__}.REX object'])
 
         if self.pickler is not pickle._Pickler:
             # Python implementation is less strict and also accepts iterables.
@@ -2105,7 +2003,7 @@ class AbstractPicklingErrorTests:
                     self.assertEqual(str(cm.exception),
                         'dict items iterator must return 2-tuples')
                     self.assertEqual(cm.exception.__notes__, [
-                        'when serializing test.pickletester.REX object'])
+                        f'when serializing {REX.__module__}.REX object'])
 
     def test_unpickleable_object_dict_items(self):
         obj = REX_seven({'a': UNPICKLEABLE})
@@ -2114,8 +2012,8 @@ class AbstractPicklingErrorTests:
                 with self.assertRaises(CustomError) as cm:
                     self.dumps(obj, proto)
                 self.assertEqual(cm.exception.__notes__, [
-                    "when serializing test.pickletester.REX_seven item 'a'",
-                    'when serializing test.pickletester.REX_seven object'])
+                    f"when serializing {REX_seven.__module__}.REX_seven item 'a'",
+                    f'when serializing {REX_seven.__module__}.REX_seven object'])
 
     def test_unpickleable_list_items(self):
         obj = [1, [2, 3, UNPICKLEABLE]]
@@ -2208,15 +2106,15 @@ class AbstractPicklingErrorTests:
     def test_global_lookup_error(self):
         # Global name does not exist
         obj = REX('spam')
-        obj.__module__ = __name__
+        obj.__module__ = 'test.picklecommon'
         for proto in protocols:
             with self.subTest(proto=proto):
                 with self.assertRaises(pickle.PicklingError) as cm:
                     self.dumps(obj, proto)
                 self.assertEqual(str(cm.exception),
-                    f"Can't pickle {obj!r}: it's not found as {__name__}.spam")
+                    f"Can't pickle {obj!r}: it's not found as test.picklecommon.spam")
                 self.assertEqual(str(cm.exception.__context__),
-                    f"module '{__name__}' has no attribute 'spam'")
+                    "module 'test.picklecommon' has no attribute 'spam'")
 
         obj.__module__ = 'nonexisting'
         for proto in protocols:
@@ -2371,6 +2269,7 @@ class AbstractPicklingErrorTests:
         with self.assertRaises(TypeError):
             self.dumps(c)
 
+    @support.skip_if_unlimited_stack_size
     @no_tracing
     def test_bad_getattr(self):
         # Issue #3514: crash when there is an infinite loop in __getattr__
@@ -2381,6 +2280,7 @@ class AbstractPicklingErrorTests:
         for proto in range(2, pickle.HIGHEST_PROTOCOL + 1):
             s = self.dumps(x, proto)
 
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; AttributeError: module 'pickle' has no attribute 'PickleBuffer'
     def test_picklebuffer_error(self):
         # PickleBuffer forbidden with protocol < 5
         pb = pickle.PickleBuffer(b"foobar")
@@ -2437,7 +2337,7 @@ class AbstractPicklingErrorTests:
     def test_bad_ext_code(self):
         # This should never happen in normal circumstances, because the type
         # and the value of the extension code is checked in copyreg.add_extension().
-        key = (__name__, 'MyList')
+        key = (MyList.__module__, 'MyList')
         def check(code, exc):
             assert key not in copyreg._extension_registry
             assert code not in copyreg._inverted_registry
@@ -2459,6 +2359,7 @@ class AbstractPicklingErrorTests:
 class AbstractPickleTests:
     # Subclass must define self.dumps, self.loads.
 
+    py_version = sys.version_info  # for test_xpickle
     optimized = False
 
     _testdata = AbstractUnpickleTests._testdata
@@ -2471,24 +2372,33 @@ class AbstractPickleTests:
     def test_misc(self):
         # test various datatypes not tested by testdata
         for proto in protocols:
-            x = myint(4)
-            s = self.dumps(x, proto)
-            y = self.loads(s)
-            self.assert_is_copy(x, y)
+            with self.subTest('myint', proto=proto):
+                if self.py_version < (3, 0) and proto < 2:
+                    self.skipTest('int subclasses are not interoperable with Python 2')
+                x = myint(4)
+                s = self.dumps(x, proto)
+                y = self.loads(s)
+                self.assert_is_copy(x, y)
 
-            x = (1, ())
-            s = self.dumps(x, proto)
-            y = self.loads(s)
-            self.assert_is_copy(x, y)
+            with self.subTest('tuple', proto=proto):
+                x = (1, ())
+                s = self.dumps(x, proto)
+                y = self.loads(s)
+                self.assert_is_copy(x, y)
 
-            x = initarg(1, x)
-            s = self.dumps(x, proto)
-            y = self.loads(s)
-            self.assert_is_copy(x, y)
+            with self.subTest('initarg', proto=proto):
+                if self.py_version < (3, 0):
+                    self.skipTest('"classic" classes are not interoperable with Python 2')
+                x = initarg(1, x)
+                s = self.dumps(x, proto)
+                y = self.loads(s)
+                self.assert_is_copy(x, y)
 
         # XXX test __reduce__ protocol?
 
     def test_roundtrip_equality(self):
+        if self.py_version < (3, 0):
+            self.skipTest('"classic" classes are not interoperable with Python 2')
         expected = self._testdata
         for proto in protocols:
             s = self.dumps(expected, proto)
@@ -2685,6 +2595,8 @@ class AbstractPickleTests:
         self._test_recursive_tuple_and_dict_key(REX_seven, asdict=lambda x: x.table)
 
     def test_recursive_set(self):
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
         # Set containing an immutable object containing the original set.
         y = set()
         y.add(K(y))
@@ -2708,6 +2620,8 @@ class AbstractPickleTests:
 
     def test_recursive_inst(self):
         # Mutable object containing itself.
+        if self.py_version < (3, 0):
+            self.skipTest('"classic" classes are not interoperable with Python 2')
         i = Object()
         i.attr = i
         for proto in protocols:
@@ -2718,6 +2632,8 @@ class AbstractPickleTests:
             self.assertIs(x.attr, x)
 
     def test_recursive_multi(self):
+        if self.py_version < (3, 0):
+            self.skipTest('"classic" classes are not interoperable with Python 2')
         l = []
         d = {1:l}
         i = Object()
@@ -2732,39 +2648,49 @@ class AbstractPickleTests:
             self.assertEqual(list(x[0].attr.keys()), [1])
             self.assertIs(x[0].attr[1], x)
 
-    def _test_recursive_collection_and_inst(self, factory):
+    def _test_recursive_collection_and_inst(self, factory, oldminproto=None):
+        if self.py_version < (3, 0):
+            self.skipTest('"classic" classes are not interoperable with Python 2')
         # Mutable object containing a collection containing the original
         # object.
         o = Object()
         o.attr = factory([o])
         t = type(o.attr)
-        for proto in protocols:
-            s = self.dumps(o, proto)
-            x = self.loads(s)
-            self.assertIsInstance(x.attr, t)
-            self.assertEqual(len(x.attr), 1)
-            self.assertIsInstance(list(x.attr)[0], Object)
-            self.assertIs(list(x.attr)[0], x)
+        with self.subTest('obj -> {t.__name__} -> obj'):
+            for proto in protocols:
+                with self.subTest(proto=proto):
+                    s = self.dumps(o, proto)
+                    x = self.loads(s)
+                    self.assertIsInstance(x.attr, t)
+                    self.assertEqual(len(x.attr), 1)
+                    self.assertIsInstance(list(x.attr)[0], Object)
+                    self.assertIs(list(x.attr)[0], x)
 
         # Collection containing a mutable object containing the original
         # collection.
         o = o.attr
-        for proto in protocols:
-            s = self.dumps(o, proto)
-            x = self.loads(s)
-            self.assertIsInstance(x, t)
-            self.assertEqual(len(x), 1)
-            self.assertIsInstance(list(x)[0], Object)
-            self.assertIs(list(x)[0].attr, x)
+        with self.subTest(f'{t.__name__} -> obj -> {t.__name__}'):
+            if self.py_version < (3, 4) and oldminproto is None:
+                self.skipTest('not supported in Python < 3.4')
+            for proto in protocols:
+                with self.subTest(proto=proto):
+                    if self.py_version < (3, 4) and proto < oldminproto:
+                        self.skipTest(f'requires protocol {oldminproto} in Python < 3.4')
+                    s = self.dumps(o, proto)
+                    x = self.loads(s)
+                    self.assertIsInstance(x, t)
+                    self.assertEqual(len(x), 1)
+                    self.assertIsInstance(list(x)[0], Object)
+                    self.assertIs(list(x)[0].attr, x)
 
     def test_recursive_list_and_inst(self):
-        self._test_recursive_collection_and_inst(list)
+        self._test_recursive_collection_and_inst(list, oldminproto=0)
 
     def test_recursive_tuple_and_inst(self):
-        self._test_recursive_collection_and_inst(tuple)
+        self._test_recursive_collection_and_inst(tuple, oldminproto=0)
 
     def test_recursive_dict_and_inst(self):
-        self._test_recursive_collection_and_inst(dict.fromkeys)
+        self._test_recursive_collection_and_inst(dict.fromkeys, oldminproto=0)
 
     def test_recursive_set_and_inst(self):
         self._test_recursive_collection_and_inst(set)
@@ -2773,13 +2699,13 @@ class AbstractPickleTests:
         self._test_recursive_collection_and_inst(frozenset)
 
     def test_recursive_list_subclass_and_inst(self):
-        self._test_recursive_collection_and_inst(MyList)
+        self._test_recursive_collection_and_inst(MyList, oldminproto=2)
 
     def test_recursive_tuple_subclass_and_inst(self):
         self._test_recursive_collection_and_inst(MyTuple)
 
     def test_recursive_dict_subclass_and_inst(self):
-        self._test_recursive_collection_and_inst(MyDict.fromkeys)
+        self._test_recursive_collection_and_inst(MyDict.fromkeys, oldminproto=2)
 
     def test_recursive_set_subclass_and_inst(self):
         self._test_recursive_collection_and_inst(MySet)
@@ -2839,6 +2765,8 @@ class AbstractPickleTests:
 
     def test_unicode_memoization(self):
         # Repeated str is re-used (even when escapes added).
+        if self.py_version < (3, 0):
+            self.skipTest('not supported in Python < 3.0')
         for proto in protocols:
             for s in '', 'xyz', 'xyz\n', 'x\\yz', 'x\xa1yz\r':
                 p = self.dumps((s, s), proto)
@@ -2858,23 +2786,27 @@ class AbstractPickleTests:
                 self.assert_is_copy(s, self.loads(p))
 
     def test_bytes_memoization(self):
+        array_types = [bytes]
+        if self.py_version >= (3, 4):
+            array_types += [ZeroCopyBytes]
         for proto in protocols:
-            for array_type in [bytes, ZeroCopyBytes]:
+            for array_type in array_types:
                 for s in b'', b'xyz', b'xyz'*100:
+                    b = array_type(s)
+                    expected = (b, b) if self.py_version >= (3, 0) else (b.decode(),)*2
                     with self.subTest(proto=proto, array_type=array_type, s=s, independent=False):
-                        b = array_type(s)
                         p = self.dumps((b, b), proto)
                         x, y = self.loads(p)
                         self.assertIs(x, y)
-                        self.assert_is_copy((b, b), (x, y))
+                        self.assert_is_copy(expected, (x, y))
 
+                    b2 = array_type(s)
                     with self.subTest(proto=proto, array_type=array_type, s=s, independent=True):
-                        b1, b2 = array_type(s), array_type(s)
-                        p = self.dumps((b1, b2), proto)
-                        # Note that (b1, b2) = self.loads(p) might have identical
-                        # components, i.e., b1 is b2, but this is not always the
+                        p = self.dumps((b, b2), proto)
+                        # Note that (b, b2) = self.loads(p) might have identical
+                        # components, i.e., b is b2, but this is not always the
                         # case if the content is large (equality still holds).
-                        self.assert_is_copy((b1, b2), self.loads(p))
+                        self.assert_is_copy(expected, self.loads(p))
 
     def test_bytearray(self):
         for proto in protocols:
@@ -2896,8 +2828,11 @@ class AbstractPickleTests:
                     self.assertTrue(opcode_in_pickle(pickle.BYTEARRAY8, p))
 
     def test_bytearray_memoization(self):
+        array_types = [bytearray]
+        if self.py_version >= (3, 4):
+            array_types += [ZeroCopyBytearray]
         for proto in protocols:
-            for array_type in [bytearray, ZeroCopyBytearray]:
+            for array_type in array_types:
                 for s in b'', b'xyz', b'xyz'*100:
                     with self.subTest(proto=proto, array_type=array_type, s=s, independent=False):
                         b = array_type(s)
@@ -2921,6 +2856,53 @@ class AbstractPickleTests:
                         self.assertIsNot(b2a, b2b)
                         self.assert_is_copy(b2a, b2b)
 
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; AttributeError: module 'pickle' has no attribute 'PickleBuffer'
+    def test_picklebuffer_memoization(self):
+        if self.py_version < (3, 8):
+            self.skipTest('not supported in Python < 3.8')
+        array_types = [bytes, bytearray]
+        for proto in range(5, pickle.HIGHEST_PROTOCOL + 1):
+            for array_type in array_types:
+                for s in b'', b'xyz', b'xyz'*100:
+                    with self.subTest(proto=proto, array_type=array_type, s=s, independent=False):
+                        b = pickle.PickleBuffer(array_type(s))
+                        p = self.dumps((b, b), proto)
+                        b1, b2 = self.loads(p)
+                        self.assertIs(b1, b2)
+
+                    with self.subTest(proto=proto, array_type=array_type, s=s, independent=True):
+                        b = array_type(s)
+                        b1a = pickle.PickleBuffer(b)
+                        b2a = pickle.PickleBuffer(b)
+                        p = self.dumps((b1a, b2a), proto)
+                        b1b, b2b = self.loads(p)
+                        if array_type is not bytes:
+                            self.assertIsNot(b1b, b2b)
+                        self.assert_is_copy(b1b, b)
+                        self.assert_is_copy(b2b, b)
+
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; AttributeError: module 'pickle' has no attribute 'PickleBuffer'
+    def test_empty_picklebuffer_memoization(self):
+        # gh-148914: Empty writable PickleBuffer memoized an empty bytearray
+        # with the id of b'' (a singleton in CPython).
+        if self.py_version < (3, 8):
+            self.skipTest('not supported in Python < 3.8')
+        for proto in range(5, pickle.HIGHEST_PROTOCOL + 1):
+            for readonly in False, True:
+                with self.subTest(proto=proto, readonly=readonly):
+                    b = b''
+                    ba = bytearray()
+                    buf = pickle.PickleBuffer(b if readonly else ba)
+                    p = self.dumps((buf, b, ba), proto)
+                    buf, b, ba = self.loads(p)
+                    array_type = bytes if readonly else bytearray
+                    self.assertIsInstance(buf, array_type)
+                    self.assertIsInstance(b, bytes)
+                    self.assertIsInstance(ba, bytearray)
+                    self.assertEqual(buf, b'')
+                    self.assertEqual(b, b'')
+                    self.assertEqual(ba, b'')
+
     def test_ints(self):
         for proto in protocols:
             n = sys.maxsize
@@ -2971,12 +2953,17 @@ class AbstractPickleTests:
 
     def test_reduce(self):
         for proto in protocols:
-            inst = AAA()
-            dumped = self.dumps(inst, proto)
-            loaded = self.loads(dumped)
-            self.assertEqual(loaded, REDUCE_A)
+            with self.subTest(proto=proto):
+                if self.py_version < (3, 4) and proto < 3:
+                    self.skipTest('str is not interoperable with Python < 3.4')
+                inst = AAA()
+                dumped = self.dumps(inst, proto)
+                loaded = self.loads(dumped)
+                self.assertEqual(loaded, REDUCE_A)
 
     def test_getinitargs(self):
+        if self.py_version < (3, 0):
+            self.skipTest('"classic" classes are not interoperable with Python 2')
         for proto in protocols:
             inst = initarg(1, 2)
             dumped = self.dumps(inst, proto)
@@ -2984,6 +2971,7 @@ class AbstractPickleTests:
             self.assert_is_copy(inst, loaded)
 
     def test_metaclass(self):
+        self.assertEqual(type(use_metaclass), metaclass)
         a = use_metaclass()
         for proto in protocols:
             s = self.dumps(a, proto)
@@ -3008,6 +2996,10 @@ class AbstractPickleTests:
             s = self.dumps(t, proto)
             u = self.loads(s)
             self.assert_is_copy(t, u)
+            if self.py_version < (3, 4):
+                # module 'os' has no attributes '_make_stat_result' and
+                # '_make_statvfs_result'
+                continue
             t = os.stat(os.curdir)
             s = self.dumps(t, proto)
             u = self.loads(s)
@@ -3019,52 +3011,111 @@ class AbstractPickleTests:
                 self.assert_is_copy(t, u)
 
     def test_ellipsis(self):
+        if self.py_version < (3, 3):
+            self.skipTest('not supported in Python < 3.3')
         for proto in protocols:
-            s = self.dumps(..., proto)
-            u = self.loads(s)
-            self.assertIs(..., u)
+            with self.subTest(proto=proto):
+                s = self.dumps(..., proto)
+                u = self.loads(s)
+                self.assertIs(..., u)
 
     def test_notimplemented(self):
+        if self.py_version < (3, 3):
+            self.skipTest('not supported in Python < 3.3')
         for proto in protocols:
-            s = self.dumps(NotImplemented, proto)
-            u = self.loads(s)
-            self.assertIs(NotImplemented, u)
+            with self.subTest(proto=proto):
+                s = self.dumps(NotImplemented, proto)
+                u = self.loads(s)
+                self.assertIs(NotImplemented, u)
 
     def test_singleton_types(self):
         # Issue #6477: Test that types of built-in singletons can be pickled.
+        if self.py_version < (3, 3):
+            self.skipTest('not supported in Python < 3.3')
         singletons = [None, ..., NotImplemented]
         for singleton in singletons:
+            t = type(singleton)
             for proto in protocols:
-                s = self.dumps(type(singleton), proto)
-                u = self.loads(s)
-                self.assertIs(type(singleton), u)
-
-    def test_builtin_types(self):
-        for t in builtins.__dict__.values():
-            if isinstance(t, type) and not issubclass(t, BaseException):
-                for proto in protocols:
-                    s = self.dumps(t, proto)
-                    self.assertIs(self.loads(s), t)
-
-    def test_builtin_exceptions(self):
-        for t in builtins.__dict__.values():
-            if isinstance(t, type) and issubclass(t, BaseException):
-                for proto in protocols:
+                with self.subTest(name=t.__name__, proto=proto):
                     s = self.dumps(t, proto)
                     u = self.loads(s)
-                    if proto <= 2 and issubclass(t, OSError) and t is not BlockingIOError:
-                        self.assertIs(u, OSError)
-                    elif proto <= 2 and issubclass(t, ImportError):
-                        self.assertIs(u, ImportError)
-                    else:
-                        self.assertIs(u, t)
+                    self.assertIs(t, u)
+
+    def test_builtin_types(self):
+        new_names = {
+            'bytes': (3, 0),
+            'BuiltinImporter': (3, 3),
+            'str': (3, 4),  # not interoperable with Python < 3.4
+        }
+        for t in builtins.__dict__.values():
+            if isinstance(t, type) and not issubclass(t, BaseException):
+                if t.__name__ in new_names and self.py_version < new_names[t.__name__]:
+                    continue
+                for proto in protocols:
+                    with self.subTest(name=t.__name__, proto=proto):
+                        s = self.dumps(t, proto)
+                        self.assertIs(self.loads(s), t)
+
+    def test_builtin_exceptions(self):
+        new_names = {
+            'BlockingIOError': (3, 3),
+            'BrokenPipeError': (3, 3),
+            'ChildProcessError': (3, 3),
+            'ConnectionError': (3, 3),
+            'ConnectionAbortedError': (3, 3),
+            'ConnectionRefusedError': (3, 3),
+            'ConnectionResetError': (3, 3),
+            'FileExistsError': (3, 3),
+            'FileNotFoundError': (3, 3),
+            'InterruptedError': (3, 3),
+            'IsADirectoryError': (3, 3),
+            'NotADirectoryError': (3, 3),
+            'PermissionError': (3, 3),
+            'ProcessLookupError': (3, 3),
+            'TimeoutError': (3, 3),
+            'RecursionError': (3, 5),
+            'StopAsyncIteration': (3, 5),
+            'ModuleNotFoundError': (3, 6),
+            'EncodingWarning': (3, 10),
+            'BaseExceptionGroup': (3, 11),
+            'ExceptionGroup': (3, 11),
+            '_IncompleteInputError': (3, 13),
+            'PythonFinalizationError': (3, 13),
+        }
+        for t in builtins.__dict__.values():
+            if isinstance(t, type) and issubclass(t, BaseException):
+                if t.__name__ in new_names and self.py_version < new_names[t.__name__]:
+                    continue
+                for proto in protocols:
+                    with self.subTest(name=t.__name__, proto=proto):
+                        if self.py_version < (3, 3) and proto < 3:
+                            self.skipTest('exception classes are not interoperable with Python < 3.3')
+                        s = self.dumps(t, proto)
+                        u = self.loads(s)
+                        if proto <= 2 and issubclass(t, OSError) and t is not BlockingIOError:
+                            self.assertIs(u, OSError)
+                        elif proto <= 2 and issubclass(t, ImportError):
+                            self.assertIs(u, ImportError)
+                        else:
+                            self.assertIs(u, t)
 
     def test_builtin_functions(self):
+        new_names = {
+            '__build_class__': (3, 0),
+            'ascii': (3, 0),
+            'exec': (3, 0),
+            'breakpoint': (3, 7),
+            'aiter': (3, 10),
+            'anext': (3, 10),
+        }
         for t in builtins.__dict__.values():
             if isinstance(t, types.BuiltinFunctionType):
+                if t.__name__ in new_names and self.py_version < new_names[t.__name__]:
+                    continue
                 for proto in protocols:
-                    s = self.dumps(t, proto)
-                    self.assertIs(self.loads(s), t)
+                    with self.subTest(name=t.__name__, proto=proto):
+                        s = self.dumps(t, proto)
+                        self.assertIs(self.loads(s), t)
 
     # Tests for protocol 2
 
@@ -3077,6 +3128,9 @@ class AbstractPickleTests:
             else:
                 self.assertEqual(count_opcode(pickle.PROTO, pickled), 0)
 
+    def test_bad_proto(self):
+        if self.py_version < (3, 8):
+            self.skipTest('no protocol validation in Python < 3.8')
         oob = protocols[-1] + 1     # a future protocol
         build_none = pickle.NONE + pickle.STOP
         badpickle = pickle.PROTO + bytes([oob]) + build_none
@@ -3188,57 +3242,65 @@ class AbstractPickleTests:
     def test_newobj_generic(self):
         for proto in protocols:
             for C in myclasses:
-                B = C.__base__
-                x = C(C.sample)
-                x.foo = 42
-                s = self.dumps(x, proto)
-                y = self.loads(s)
-                detail = (proto, C, B, x, y, type(y))
-                self.assert_is_copy(x, y) # XXX revisit
-                self.assertEqual(B(x), B(y), detail)
-                self.assertEqual(x.__dict__, y.__dict__, detail)
+                with self.subTest(proto=proto, C=C):
+                    if self.py_version < (3, 0) and proto < 2 and C in (MyInt, MyStr):
+                        self.skipTest('int and str subclasses are not interoperable with Python 2')
+                    if (3, 0) <= self.py_version < (3, 4) and proto < 2 and C in (MyStr, MyUnicode):
+                        self.skipTest('str subclasses are not interoperable with Python < 3.4')
+                    B = C.__base__
+                    x = C(C.sample)
+                    x.foo = 42
+                    s = self.dumps(x, proto)
+                    y = self.loads(s)
+                    detail = (proto, C, B, x, y, type(y))
+                    self.assert_is_copy(x, y) # XXX revisit
+                    self.assertEqual(B(x), B(y), detail)
+                    self.assertEqual(x.__dict__, y.__dict__, detail)
 
     def test_newobj_proxies(self):
         # NEWOBJ should use the __class__ rather than the raw type
         classes = myclasses[:]
         # Cannot create weakproxies to these classes
-        for c in (MyInt, MyTuple):
+        for c in (MyInt, MyLong, MyTuple):
             classes.remove(c)
         for proto in protocols:
             for C in classes:
-                B = C.__base__
-                x = C(C.sample)
-                x.foo = 42
-                p = weakref.proxy(x)
-                s = self.dumps(p, proto)
-                y = self.loads(s)
-                self.assertEqual(type(y), type(x))  # rather than type(p)
-                detail = (proto, C, B, x, y, type(y))
-                self.assertEqual(B(x), B(y), detail)
-                self.assertEqual(x.__dict__, y.__dict__, detail)
+                with self.subTest(proto=proto, C=C):
+                    if self.py_version < (3, 4) and proto < 3 and C in (MyStr, MyUnicode):
+                        self.skipTest('str subclasses are not interoperable with Python < 3.4')
+                    B = C.__base__
+                    x = C(C.sample)
+                    x.foo = 42
+                    p = weakref.proxy(x)
+                    s = self.dumps(p, proto)
+                    y = self.loads(s)
+                    self.assertEqual(type(y), type(x))  # rather than type(p)
+                    detail = (proto, C, B, x, y, type(y))
+                    self.assertEqual(B(x), B(y), detail)
+                    self.assertEqual(x.__dict__, y.__dict__, detail)
 
     def test_newobj_overridden_new(self):
         # Test that Python class with C implemented __new__ is pickleable
         for proto in protocols:
-            x = MyIntWithNew2(1)
-            x.foo = 42
-            s = self.dumps(x, proto)
-            y = self.loads(s)
-            self.assertIs(type(y), MyIntWithNew2)
-            self.assertEqual(int(y), 1)
-            self.assertEqual(y.foo, 42)
+            with self.subTest(proto=proto):
+                if self.py_version < (3, 0) and proto < 2:
+                    self.skipTest('int subclasses are not interoperable with Python 2')
+                x = MyIntWithNew2(1)
+                x.foo = 42
+                s = self.dumps(x, proto)
+                y = self.loads(s)
+                self.assertIs(type(y), MyIntWithNew2)
+                self.assertEqual(int(y), 1)
+                self.assertEqual(y.foo, 42)
 
     def test_newobj_not_class(self):
         # Issue 24552
-        global SimpleNewObj
-        save = SimpleNewObj
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
         o = SimpleNewObj.__new__(SimpleNewObj)
         b = self.dumps(o, 4)
-        try:
-            SimpleNewObj = 42
+        with support.swap_attr(picklecommon, 'SimpleNewObj', 42):
             self.assertRaises((TypeError, pickle.UnpicklingError), self.loads, b)
-        finally:
-            SimpleNewObj = save
 
     # Register a type with copyreg, with extension code extcode.  Pickle
     # an object of that type.  Check that the resulting pickle uses opcode
@@ -3247,14 +3309,14 @@ class AbstractPickleTests:
     def produce_global_ext(self, extcode, opcode):
         e = ExtensionSaver(extcode)
         try:
-            copyreg.add_extension(__name__, "MyList", extcode)
+            copyreg.add_extension(MyList.__module__, "MyList", extcode)
             x = MyList([1, 2, 3])
             x.foo = 42
             x.bar = "hello"
 
             # Dump using protocol 1 for comparison.
             s1 = self.dumps(x, 1)
-            self.assertIn(__name__.encode("utf-8"), s1)
+            self.assertIn(MyList.__module__.encode(), s1)
             self.assertIn(b"MyList", s1)
             self.assertFalse(opcode_in_pickle(opcode, s1))
 
@@ -3263,7 +3325,7 @@ class AbstractPickleTests:
 
             # Dump using protocol 2 for test.
             s2 = self.dumps(x, 2)
-            self.assertNotIn(__name__.encode("utf-8"), s2)
+            self.assertNotIn(MyList.__module__.encode(), s2)
             self.assertNotIn(b"MyList", s2)
             self.assertEqual(opcode_in_pickle(opcode, s2), True, repr(s2))
 
@@ -3361,14 +3423,20 @@ class AbstractPickleTests:
         x.abc = 666
         for proto in protocols:
             with self.subTest(proto=proto):
+                if self.py_version < (3, 0) and proto < 2:
+                    self.skipTest('int subclasses are not interoperable with Python 2')
                 s = self.dumps(x, proto)
                 if proto < 1:
-                    self.assertIn(b'\nI64206', s)  # INT
+                    if self.py_version >= (3, 7):
+                        self.assertIn(b'\nI64206', s)  # INT
+                    else:  # for test_xpickle
+                        self.assertIn(b'64206', s)  # INT or LONG
                 else:
                     self.assertIn(b'M\xce\xfa', s)  # BININT2
-                self.assertEqual(opcode_in_pickle(pickle.NEWOBJ, s),
-                                 2 <= proto)
-                self.assertFalse(opcode_in_pickle(pickle.NEWOBJ_EX, s))
+                if not (self.py_version < (3, 5) and proto == 4):
+                    self.assertEqual(opcode_in_pickle(pickle.NEWOBJ, s),
+                                     2 <= proto)
+                    self.assertFalse(opcode_in_pickle(pickle.NEWOBJ_EX, s))
                 y = self.loads(s)   # will raise TypeError if __init__ called
                 self.assert_is_copy(x, y)
 
@@ -3377,29 +3445,45 @@ class AbstractPickleTests:
         x.abc = 666
         for proto in protocols:
             with self.subTest(proto=proto):
+                if self.py_version < (3, 0) and proto < 2:
+                    self.skipTest('int subclasses are not interoperable with Python 2')
                 s = self.dumps(x, proto)
                 if proto < 1:
-                    self.assertIn(b'\nI64206', s)  # INT
+                    if self.py_version >= (3, 7):
+                        self.assertIn(b'\nI64206', s)  # INT
+                    else:  # for test_xpickle
+                        self.assertIn(b'64206', s)  # INT or LONG
                 elif proto < 2:
                     self.assertIn(b'M\xce\xfa', s)  # BININT2
                 elif proto < 4:
-                    self.assertIn(b'X\x04\x00\x00\x00FACE', s)  # BINUNICODE
+                    if self.py_version >= (3, 0):
+                        self.assertIn(b'X\x04\x00\x00\x00FACE', s)  # BINUNICODE
+                    else:  # for test_xpickle
+                        self.assertIn(b'U\x04FACE', s)  # SHORT_BINSTRING
                 else:
                     self.assertIn(b'\x8c\x04FACE', s)  # SHORT_BINUNICODE
-                self.assertEqual(opcode_in_pickle(pickle.NEWOBJ, s),
-                                 2 <= proto)
-                self.assertFalse(opcode_in_pickle(pickle.NEWOBJ_EX, s))
+                if not (self.py_version < (3, 5) and proto == 4):
+                    self.assertEqual(opcode_in_pickle(pickle.NEWOBJ, s),
+                                     2 <= proto)
+                    self.assertFalse(opcode_in_pickle(pickle.NEWOBJ_EX, s))
                 y = self.loads(s)   # will raise TypeError if __init__ called
                 self.assert_is_copy(x, y)
 
     def test_complex_newobj_ex(self):
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
         x = ComplexNewObjEx.__new__(ComplexNewObjEx, 0xface)  # avoid __init__
         x.abc = 666
         for proto in protocols:
             with self.subTest(proto=proto):
+                if self.py_version < (3, 6) and proto < 4:
+                    self.skipTest('requires protocol 4 in Python < 3.6')
                 s = self.dumps(x, proto)
                 if proto < 1:
-                    self.assertIn(b'\nI64206', s)  # INT
+                    if self.py_version >= (3, 7):
+                        self.assertIn(b'\nI64206', s)  # INT
+                    else:  # for test_xpickle
+                        self.assertIn(b'64206', s)  # INT or LONG
                 elif proto < 2:
                     self.assertIn(b'M\xce\xfa', s)  # BININT2
                 elif proto < 4:
@@ -3487,6 +3571,8 @@ class AbstractPickleTests:
     def test_attribute_name_interning(self):
         # Test that attribute names of pickled objects are interned when
         # unpickling.
+        if self.py_version < (3, 0):
+            self.skipTest('"classic" classes are not interoperable with Python 2')
         for proto in protocols:
             x = C()
             x.foo = 42
@@ -3516,10 +3602,14 @@ class AbstractPickleTests:
             dumped = self.dumps(data, proto)
             loaded = self.loads(dumped)
             self.assertEqual(len(loaded), len(data))
+            if self.py_version < (3, 0):
+                data = (1, min, 'xy' * (30 * 1024), len)
             self.assertEqual(loaded, data)
 
     def test_int_pickling_efficiency(self):
         # Test compacity of int representation (see issue #12744)
+        if self.py_version < (3, 3):
+            self.skipTest('not supported in Python < 3.3')
         for proto in protocols:
             with self.subTest(proto=proto):
                 pickles = [self.dumps(2**n, proto) for n in range(70)]
@@ -3540,10 +3630,13 @@ class AbstractPickleTests:
         # Issue #17720
         obj = REX_six([1, 2, 3])
         for proto in protocols:
-            if proto == 0:
-                self._check_pickling_with_opcode(obj, pickle.APPEND, proto)
-            else:
-                self._check_pickling_with_opcode(obj, pickle.APPENDS, proto)
+            with self.subTest(proto=proto):
+                if proto == 0:
+                    self._check_pickling_with_opcode(obj, pickle.APPEND, proto)
+                else:
+                    if self.py_version < (3, 0):
+                        self.skipTest('not supported in Python 2')
+                    self._check_pickling_with_opcode(obj, pickle.APPENDS, proto)
 
     def test_setitems_on_non_dicts(self):
         obj = REX_seven({1: -1, 2: -2, 3: -3})
@@ -3608,6 +3701,8 @@ class AbstractPickleTests:
     @support.skip_if_pgo_task
     @support.requires_resource('cpu')
     def test_framing_many_objects(self):
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
         obj = list(range(10**5))
         for proto in range(4, pickle.HIGHEST_PROTOCOL + 1):
             with self.subTest(proto=proto):
@@ -3623,6 +3718,8 @@ class AbstractPickleTests:
                 self.check_frame_opcodes(pickled)
 
     def test_framing_large_objects(self):
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
         N = 1024 * 1024
         small_items = [[i] for i in range(10)]
         obj = [b'x' * N, *small_items, b'y' * N, 'z' * N]
@@ -3648,15 +3745,16 @@ class AbstractPickleTests:
                                      [len(x) for x in unpickled])
                     # Perform full equality check if the lengths match.
                     self.assertEqual(obj, unpickled)
-                    n_frames = count_opcode(pickle.FRAME, pickled)
-                    # A single frame for small objects between
-                    # first two large objects.
-                    self.assertEqual(n_frames, 1)
-                    self.check_frame_opcodes(pickled)
+                    if self.py_version >= (3, 7):
+                        n_frames = count_opcode(pickle.FRAME, pickled)
+                        # A single frame for small objects between
+                        # first two large objects.
+                        self.assertEqual(n_frames, 1)
+                        self.check_frame_opcodes(pickled)
 
     def test_optional_frames(self):
-        if pickle.HIGHEST_PROTOCOL < 4:
-            return
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
 
         def remove_frames(pickled, keep_frame=None):
             """Remove frame opcodes from the given pickle."""
@@ -3698,6 +3796,9 @@ class AbstractPickleTests:
 
     @support.skip_if_pgo_task
     def test_framed_write_sizes_with_delayed_writer(self):
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
+
         class ChunkAccumulator:
             """Accumulate pickler output in a list of raw chunks."""
             def __init__(self):
@@ -3763,13 +3864,12 @@ class AbstractPickleTests:
                                  chunk_sizes)
 
     def test_nested_names(self):
-        global Nested
-        class Nested:
-            class A:
-                class B:
-                    class C:
-                        pass
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
+        # required protocol 4 in Python 3.4
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            if self.py_version < (3, 5) and proto < 4:
+                continue
             for obj in [Nested.A, Nested.A.B, Nested.A.B.C]:
                 with self.subTest(proto=proto, obj=obj):
                     unpickled = self.loads(self.dumps(obj, proto))
@@ -3800,35 +3900,21 @@ class AbstractPickleTests:
         del Recursive.ref # break reference loop
 
     def test_py_methods(self):
-        global PyMethodsTest
-        class PyMethodsTest:
-            @staticmethod
-            def cheese():
-                return "cheese"
-            @classmethod
-            def wine(cls):
-                assert cls is PyMethodsTest
-                return "wine"
-            def biscuits(self):
-                assert isinstance(self, PyMethodsTest)
-                return "biscuits"
-            class Nested:
-                "Nested class"
-                @staticmethod
-                def ketchup():
-                    return "ketchup"
-                @classmethod
-                def maple(cls):
-                    assert cls is PyMethodsTest.Nested
-                    return "maple"
-                def pie(self):
-                    assert isinstance(self, PyMethodsTest.Nested)
-                    return "pie"
-
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
         py_methods = (
-            PyMethodsTest.cheese,
             PyMethodsTest.wine,
             PyMethodsTest().biscuits,
+        )
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            for method in py_methods:
+                with self.subTest(proto=proto, method=method):
+                    unpickled = self.loads(self.dumps(method, proto))
+                    self.assertEqual(method(), unpickled())
+
+        # required protocol 4 in Python 3.4
+        py_methods = (
+            PyMethodsTest.cheese,
             PyMethodsTest.Nested.ketchup,
             PyMethodsTest.Nested.maple,
             PyMethodsTest.Nested().pie
@@ -3838,6 +3924,8 @@ class AbstractPickleTests:
             (PyMethodsTest.Nested.pie, PyMethodsTest.Nested)
         )
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            if self.py_version < (3, 5) and proto < 4:
+                continue
             for method in py_methods:
                 with self.subTest(proto=proto, method=method):
                     unpickled = self.loads(self.dumps(method, proto))
@@ -3858,11 +3946,8 @@ class AbstractPickleTests:
                     self.assertRaises(TypeError, self.dumps, descr, proto)
 
     def test_c_methods(self):
-        global Subclass
-        class Subclass(tuple):
-            class Nested(str):
-                pass
-
+        if self.py_version < (3, 4):
+            self.skipTest('not supported in Python < 3.4')
         c_methods = (
             # bound built-in method
             ("abcd".index, ("c",)),
@@ -3883,7 +3968,6 @@ class AbstractPickleTests:
             # subclass methods
             (Subclass([1,2,2]).count, (2,)),
             (Subclass.count, (Subclass([1,2,2]), 2)),
-            (Subclass.Nested("sweet").count, ("e",)),
             (Subclass.Nested.count, (Subclass.Nested("sweet"), "e")),
         )
         for proto in range(pickle.HIGHEST_PROTOCOL + 1):
@@ -3892,6 +3976,18 @@ class AbstractPickleTests:
                     unpickled = self.loads(self.dumps(method, proto))
                     self.assertEqual(method(*args), unpickled(*args))
 
+        # required protocol 4 in Python 3.4
+        c_methods = (
+            (Subclass.Nested("sweet").count, ("e",)),
+        )
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            if self.py_version < (3, 5) and proto < 4:
+                continue
+            for method, args in c_methods:
+                with self.subTest(proto=proto, method=method):
+                    unpickled = self.loads(self.dumps(method, proto))
+                    self.assertEqual(method(*args), unpickled(*args))
+
         descriptors = (
             bytearray.__dict__['maketrans'],  # built-in static method descriptor
             dict.__dict__['fromkeys'],  # built-in class method descriptor
@@ -3901,7 +3997,85 @@ class AbstractPickleTests:
                 with self.subTest(proto=proto, descr=descr):
                     self.assertRaises(TypeError, self.dumps, descr, proto)
 
+    def test_object_with_attrs(self):
+        obj = Object()
+        obj.a = 1
+        for proto in protocols:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.a, obj.a)
+
+    def test_object_with_slots(self):
+        obj = WithSlots()
+        obj.a = 1
+        self.assertRaises(TypeError, self.dumps, obj, 0)
+        self.assertRaises(TypeError, self.dumps, obj, 1)
+        for proto in protocols[2:]:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.a, obj.a)
+                self.assertNotHasAttr(unpickled, 'b')
+
+        obj = WithSlotsSubclass()
+        obj.a = 1
+        obj.c = 2
+        self.assertRaises(TypeError, self.dumps, obj, 0)
+        self.assertRaises(TypeError, self.dumps, obj, 1)
+        for proto in protocols[2:]:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.a, obj.a)
+                self.assertEqual(unpickled.c, obj.c)
+                self.assertNotHasAttr(unpickled, 'b')
+
+        obj = WithSlotsAndDict()
+        obj.a = 1
+        obj.c = 2
+        self.assertRaises(TypeError, self.dumps, obj, 0)
+        self.assertRaises(TypeError, self.dumps, obj, 1)
+        for proto in protocols[2:]:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.a, obj.a)
+                self.assertEqual(unpickled.c, obj.c)
+                self.assertEqual(unpickled.__dict__, obj.__dict__)
+                self.assertNotHasAttr(unpickled, 'b')
+
+    def test_object_with_private_attrs(self):
+        obj = WithPrivateAttrs(1)
+        for proto in protocols:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.get(), obj.get())
+
+        obj = WithPrivateAttrsSubclass(1, 2)
+        for proto in protocols:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.get(), obj.get())
+                self.assertEqual(unpickled.get2(), obj.get2())
+
+    def test_object_with_private_slots(self):
+        obj = WithPrivateSlots(1)
+        self.assertRaises(TypeError, self.dumps, obj, 0)
+        self.assertRaises(TypeError, self.dumps, obj, 1)
+        for proto in protocols[2:]:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.get(), obj.get())
+
+        obj = WithPrivateSlotsSubclass(1, 2)
+        self.assertRaises(TypeError, self.dumps, obj, 0)
+        self.assertRaises(TypeError, self.dumps, obj, 1)
+        for proto in protocols[2:]:
+            with self.subTest(proto=proto):
+                unpickled = self.loads(self.dumps(obj, proto))
+                self.assertEqual(unpickled.get(), obj.get())
+                self.assertEqual(unpickled.get2(), obj.get2())
+
     def test_compat_pickle(self):
+        if self.py_version < (3, 4):
+            self.skipTest("doesn't work in Python < 3.4'")
         tests = [
             (range(1, 7), '__builtin__', 'xrange'),
             (map(int, '123'), 'itertools', 'imap'),
@@ -4090,6 +4264,37 @@ class AbstractPickleTests:
         # 2-D, non-contiguous
         check_array(arr[::2])
 
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; AttributeError: module 'pickle' has no attribute 'PickleBuffer'
+    def test_concurrent_mutation_in_buffer_with_bytearray(self):
+        def factory():
+            s = b"a" * 16
+            return bytearray(s), s
+        self.do_test_concurrent_mutation_in_buffer_callback(factory)
+
+    @unittest.expectedFailure  # TODO: RUSTPYTHON; AttributeError: module 'pickle' has no attribute 'PickleBuffer'
+    def test_concurrent_mutation_in_buffer_with_memoryview(self):
+        def factory():
+            obj = memoryview(b"a" * 32)[10:26]
+            sub = b"a" * len(obj)
+            return obj, sub
+        self.do_test_concurrent_mutation_in_buffer_callback(factory)
+
+    def do_test_concurrent_mutation_in_buffer_callback(self, factory):
+        # See: https://github.com/python/cpython/issues/143308.
+        class R:
+            def __bool__(self):
+                buf.release()
+                return True
+
+        for proto in range(5, pickle.HIGHEST_PROTOCOL + 1):
+            obj, sub = factory()
+            buf = pickle.PickleBuffer(obj)
+            buffer_callback = lambda _: R()
+
+            with self.subTest(proto=proto, obj=obj, sub=sub):
+                res = self.dumps(buf, proto, buffer_callback=buffer_callback)
+                self.assertIn(sub, res)
+
     def test_evil_class_mutating_dict(self):
         # https://github.com/python/cpython/issues/92930
         from random import getrandbits
@@ -4120,6 +4325,94 @@ class AbstractPickleTests:
                     expected = "changed size during iteration"
                     self.assertIn(expected, str(e))
 
+    def fast_save_enter(self, create_data, minprotocol=0):
+        # gh-146059: Check that fast_save_leave() is called when
+        # fast_save_enter() is called.
+        if not hasattr(self, "pickler"):
+            self.skipTest("need Pickler class")
+
+        data = [create_data(i) for i in range(FAST_NESTING_LIMIT * 2)]
+        protocols = range(minprotocol, pickle.HIGHEST_PROTOCOL + 1)
+        for proto in protocols:
+            with self.subTest(proto=proto):
+                buf = io.BytesIO()
+                pickler = self.pickler(buf, protocol=proto)
+                # Enable fast mode (disables memo, enables cycle detection)
+                pickler.fast = 1
+                pickler.dump(data)
+
+                buf.seek(0)
+                data2 = self.unpickler(buf).load()
+                self.assertEqual(data2, data)
+
+    def test_fast_save_enter_tuple(self):
+        self.fast_save_enter(lambda i: (i,))
+
+    def test_fast_save_enter_list(self):
+        self.fast_save_enter(lambda i: [i])
+
+    def test_fast_save_enter_frozenset(self):
+        self.fast_save_enter(lambda i: frozenset([i]))
+
+    def test_fast_save_enter_set(self):
+        self.fast_save_enter(lambda i: set([i]))
+
+    def test_fast_save_enter_frozendict(self):
+        if self.py_version < (3, 15):
+            self.skipTest('need frozendict')
+        self.fast_save_enter(lambda i: frozendict(key=i), minprotocol=2)
+
+    def test_fast_save_enter_dict(self):
+        self.fast_save_enter(lambda i: {"key": i})
+
+    def deep_nested_struct(self, create_nested,
+                           minprotocol=0, compare_equal=True,
+                           depth=FAST_NESTING_LIMIT * 2):
+        # gh-146059: Check that fast_save_leave() is called when
+        # fast_save_enter() is called.
+        if not hasattr(self, "pickler"):
+            self.skipTest("need Pickler class")
+
+        data = None
+        for i in range(depth):
+            data = create_nested(data)
+        protocols = range(minprotocol, pickle.HIGHEST_PROTOCOL + 1)
+        for proto in protocols:
+            with self.subTest(proto=proto):
+                buf = io.BytesIO()
+                pickler = self.pickler(buf, protocol=proto)
+                # Enable fast mode (disables memo, enables cycle detection)
+                pickler.fast = 1
+                pickler.dump(data)
+
+                buf.seek(0)
+                data2 = self.unpickler(buf).load()
+                if compare_equal:
+                    self.assertEqual(data2, data)
+
+    def test_deep_nested_struct_tuple(self):
+        self.deep_nested_struct(lambda data: (data,))
+
+    def test_deep_nested_struct_list(self):
+        self.deep_nested_struct(lambda data: [data])
+
+    def test_deep_nested_struct_frozenset(self):
+        self.deep_nested_struct(lambda data: frozenset((1, data)))
+
+    def test_deep_nested_struct_set(self):
+        self.deep_nested_struct(lambda data: {K(data)},
+                                depth=FAST_NESTING_LIMIT+1,
+                                compare_equal=False)
+
+    def test_deep_nested_struct_frozendict(self):
+        if self.py_version < (3, 15):
+            self.skipTest('need frozendict')
+        self.deep_nested_struct(lambda data: frozendict(x=data),
+                                minprotocol=2)
+
+    def test_deep_nested_struct_dict(self):
+        self.deep_nested_struct(lambda data: {'x': data})
+
 
 class BigmemPickleTests:
 
@@ -4248,110 +4541,6 @@ class BigmemPickleTests:
             data = None
 
 
-# Test classes for reduce_ex
-
-class R:
-    def __init__(self, reduce=None):
-        self.reduce = reduce
-    def __reduce__(self, proto):
-        return self.reduce
-
-class REX:
-    def __init__(self, reduce_ex=None):
-        self.reduce_ex = reduce_ex
-    def __reduce_ex__(self, proto):
-        return self.reduce_ex
-
-class REX_one(object):
-    """No __reduce_ex__ here, but inheriting it from object"""
-    _reduce_called = 0
-    def __reduce__(self):
-        self._reduce_called = 1
-        return REX_one, ()
-
-class REX_two(object):
-    """No __reduce__ here, but inheriting it from object"""
-    _proto = None
-    def __reduce_ex__(self, proto):
-        self._proto = proto
-        return REX_two, ()
-
-class REX_three(object):
-    _proto = None
-    def __reduce_ex__(self, proto):
-        self._proto = proto
-        return REX_two, ()
-    def __reduce__(self):
-        raise TestFailed("This __reduce__ shouldn't be called")
-
-class REX_four(object):
-    """Calling base class method should succeed"""
-    _proto = None
-    def __reduce_ex__(self, proto):
-        self._proto = proto
-        return object.__reduce_ex__(self, proto)
-
-class REX_five(object):
-    """This one used to fail with infinite recursion"""
-    _reduce_called = 0
-    def __reduce__(self):
-        self._reduce_called = 1
-        return object.__reduce__(self)
-
-class REX_six(object):
-    """This class is used to check the 4th argument (list iterator) of
-    the reduce protocol.
-    """
-    def __init__(self, items=None):
-        self.items = items if items is not None else []
-    def __eq__(self, other):
-        return type(self) is type(other) and self.items == other.items
-    def append(self, item):
-        self.items.append(item)
-    def __reduce__(self):
-        return type(self), (), None, iter(self.items), None
-
-class REX_seven(object):
-    """This class is used to check the 5th argument (dict iterator) of
-    the reduce protocol.
-    """
-    def __init__(self, table=None):
-        self.table = table if table is not None else {}
-    def __eq__(self, other):
-        return type(self) is type(other) and self.table == other.table
-    def __setitem__(self, key, value):
-        self.table[key] = value
-    def __reduce__(self):
-        return type(self), (), None, None, iter(self.table.items())
-
-class REX_state(object):
-    """This class is used to check the 3th argument (state) of
-    the reduce protocol.
-    """
-    def __init__(self, state=None):
-        self.state = state
-    def __eq__(self, other):
-        return type(self) is type(other) and self.state == other.state
-    def __setstate__(self, state):
-        self.state = state
-    def __reduce__(self):
-        return type(self), (), self.state
-
-class REX_None:
-    """ Setting __reduce_ex__ to None should fail """
-    __reduce_ex__ = None
-
-class R_None:
-    """ Setting __reduce__ to None should fail """
-    __reduce__ = None
-
-class C_None_setstate:
-    """  Setting __setstate__ to None should fail """
-    def __getstate__(self):
-        return 1
-
-    __setstate__ = None
-
 class CustomError(Exception):
     pass
 
@@ -4361,80 +4550,17 @@ class Unpickleable:
 
 UNPICKLEABLE = Unpickleable()
 
+# For test_unpickleable_reconstructor and test_unpickleable_state_setter
 class UnpickleableCallable(Unpickleable):
     def __call__(self, *args, **kwargs):
         pass
 
-
-# Test classes for newobj
-
-class MyInt(int):
-    sample = 1
-
-class MyFloat(float):
-    sample = 1.0
-
-class MyComplex(complex):
-    sample = 1.0 + 0.0j
-
-class MyStr(str):
-    sample = "hello"
-
-class MyUnicode(str):
-    sample = "hello \u1234"
-
-class MyTuple(tuple):
-    sample = (1, 2, 3)
-
-class MyList(list):
-    sample = [1, 2, 3]
-
-class MyDict(dict):
-    sample = {"a": 1, "b": 2}
-
-class MySet(set):
-    sample = {"a", "b"}
-
-class MyFrozenSet(frozenset):
-    sample = frozenset({"a", "b"})
-
-myclasses = [MyInt, MyFloat,
-             MyComplex,
-             MyStr, MyUnicode,
-             MyTuple, MyList, MyDict, MySet, MyFrozenSet]
-
-class MyIntWithNew(int):
-    def __new__(cls, value):
-        raise AssertionError
-
-class MyIntWithNew2(MyIntWithNew):
-    __new__ = int.__new__
-
-
-class SlotList(MyList):
-    __slots__ = ["foo"]
-
-# Ruff "redefined while unused" false positive here due to `global` variables
-# being assigned (and then restored) from within test methods earlier in the file
-class SimpleNewObj(int):  # noqa: F811
-    def __init__(self, *args, **kwargs):
-        # raise an error, to make sure this isn't called
-        raise TypeError("SimpleNewObj.__init__() didn't expect to get called")
-    def __eq__(self, other):
-        return int(self) == int(other) and self.__dict__ == other.__dict__
-
-class ComplexNewObj(SimpleNewObj):
-    def __getnewargs__(self):
-        return ('%X' % self, 16)
-
-class ComplexNewObjEx(SimpleNewObj):
-    def __getnewargs_ex__(self):
-        return ('%X' % self,), {'base': 16}
-
+# For test_bad_getattr
 class BadGetattr:
     def __getattr__(self, key):
         self.foo
 
+# For test_bad_newobj_class and test_bad_newobj_ex__class
 class NoNew:
     def __getattribute__(self, name):
         if name == '__new__':
diff --git a/scripts/update_lib/deps.py b/scripts/update_lib/deps.py
index 49ddf9a87..cda511af4 100644
--- a/scripts/update_lib/deps.py
+++ b/scripts/update_lib/deps.py
@@ -323,6 +323,7 @@ DEPENDENCIES = {
             "test_pickle.py",
             "test_picklebuffer.py",
             "test_pickletools.py",
+            "picklecommon.py",
         ],
     },
     "re": {