Address review

Lib/test/test_unittest/testmock/testhelpers.py

@@ -8,8 +8,10 @@
     Mock, ANY, _CallList, patch, PropertyMock, _callable
 )
 
+from dataclasses import dataclass, field, InitVar
 from datetime import datetime
 from functools import partial
+from typing import ClassVar
 
 class SomeClass(object):
     def one(self, a, b): pass
@@ -1034,10 +1036,7 @@ def f(a): pass
         self.assertEqual(mock.mock_calls, [])
         self.assertEqual(rv.mock_calls, [])
 
-    def test_dataclass(self):
-        from dataclasses import dataclass, field, InitVar
-        from typing import ClassVar
-
+    def test_dataclass_post_init(self):
         @dataclass
         class WithPostInit:
             a: int = field(init=False)
@@ -1062,6 +1061,7 @@ def __post_init__(self):
         with self.assertRaisesRegex(AttributeError, msg):
             mock.b
 
+    def test_dataclass_default(self):
         @dataclass
         class WithDefault:
             a: int
@@ -1075,6 +1075,7 @@ class WithDefault:
                 self.assertIsInstance(mock.a, int)
                 self.assertIsInstance(mock.b, int)
 
+    def test_dataclass_with_method(self):
         @dataclass
         class WithMethod:
             a: int
@@ -1089,6 +1090,7 @@ def b(self) -> int:
                 self.assertIsInstance(mock.a, int)
                 mock.b.assert_not_called()
 
+    def test_dataclass_with_non_fields(self):
         @dataclass
         class WithNonFields:
             a: ClassVar[int]

Lib/unittest/mock.py

@@ -34,6 +34,7 @@
 import pkgutil
 from inspect import iscoroutinefunction
 import threading
+from dataclasses import fields, is_dataclass
 from types import CodeType, ModuleType, MethodType
 from unittest.util import safe_repr
 from functools import wraps, partial
@@ -2755,12 +2756,10 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
                                f'[object={spec!r}]')
     is_async_func = _is_async_func(spec)
 
-    placeholder = object()
-    entries = [(entry, placeholder) for entry in dir(spec)]
+    entries = [(entry, _missing) for entry in dir(spec)]
     # Not using `is_dataclass` to avoid an import of dataclasses module
     # for types that don't need that.
-    if is_type and instance and hasattr(spec, '__dataclass_fields__'):
-        from dataclasses import fields
+    if is_type and instance and is_dataclass(spec):
         dataclass_fields = fields(spec)
         entries.extend((f.name, f.type) for f in dataclass_fields)
         _kwargs = {'spec': [f.name for f in dataclass_fields]}
@@ -2837,7 +2836,7 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
         # AttributeError on being fetched?
         # we could be resilient against it, or catch and propagate the
         # exception when the attribute is fetched from the mock
-        if original is placeholder:
+        if original is _missing:
             try:
                 original = getattr(spec, entry)
             except AttributeError: