gh-124176: Add special support for dataclasses to create_autospec (#…

…124429)

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
@@ -1034,6 +1036,76 @@ def f(a): pass
  self.assertEqual(mock.mock_calls, [])
  self.assertEqual(rv.mock_calls, [])
 
+ def test_dataclass_post_init(self):
+ @dataclass
+ class WithPostInit:
+ a: int = field(init=False)
+ b: int = field(init=False)
+ def __post_init__(self):
+ self.a = 1
+ self.b = 2
+
+ for mock in [
+ create_autospec(WithPostInit, instance=True),
+ create_autospec(WithPostInit()),
+ ]:
+ with self.subTest(mock=mock):
+ self.assertIsInstance(mock.a, int)
+ self.assertIsInstance(mock.b, int)
+
+ # Classes do not have these fields:
+ mock = create_autospec(WithPostInit)
+ msg = "Mock object has no attribute"
+ with self.assertRaisesRegex(AttributeError, msg):
+ mock.a
+ with self.assertRaisesRegex(AttributeError, msg):
+ mock.b
+
+ def test_dataclass_default(self):
+ @dataclass
+ class WithDefault:
+ a: int
+ b: int = 0
+
+ for mock in [
+ create_autospec(WithDefault, instance=True),
+ create_autospec(WithDefault(1)),
+ ]:
+ with self.subTest(mock=mock):
+ self.assertIsInstance(mock.a, int)
+ self.assertIsInstance(mock.b, int)
+
+ def test_dataclass_with_method(self):
+ @dataclass
+ class WithMethod:
+ a: int
+ def b(self) -> int:
+ return 1
+
+ for mock in [
+ create_autospec(WithMethod, instance=True),
+ create_autospec(WithMethod(1)),
+ ]:
+ with self.subTest(mock=mock):
+ self.assertIsInstance(mock.a, int)
+ mock.b.assert_not_called()
+
+ def test_dataclass_with_non_fields(self):
+ @dataclass
+ class WithNonFields:
+ a: ClassVar[int]
+ b: InitVar[int]
+
+ msg = "Mock object has no attribute"
+ for mock in [
+ create_autospec(WithNonFields, instance=True),
+ create_autospec(WithNonFields(1)),
+ ]:
+ with self.subTest(mock=mock):
+ with self.assertRaisesRegex(AttributeError, msg):
+ mock.a
+ with self.assertRaisesRegex(AttributeError, msg):
+ mock.b
 
 class TestCallList(unittest.TestCase):
 

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
@@ -2756,7 +2757,15 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
  raise InvalidSpecError(f'Cannot autospec a Mock object. '
  f'[object={spec!r}]')
  is_async_func = _is_async_func(spec)
- _kwargs = {'spec': spec}
+
+ entries = [(entry, _missing) for entry in dir(spec)]
+ 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]}
+ else:
+ _kwargs = {'spec': spec}
+
  if spec_set:
  _kwargs = {'spec_set': spec}
  elif spec is None:
@@ -2813,7 +2822,7 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
  _name='()', _parent=mock,
  wraps=wrapped)
 
- for entry in dir(spec):
+ for entry, original in entries:
  if _is_magic(entry):
  # MagicMock already does the useful magic methods for us
  continue
@@ -2827,10 +2836,11 @@ 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
- try:
- original = getattr(spec, entry)
- except AttributeError:
- continue
+ if original is _missing:
+ try:
+ original = getattr(spec, entry)
+ except AttributeError:
+ continue
 
  child_kwargs = {'spec': original}
  # Wrap child attributes also.

Misc/NEWS.d/next/Library/2024-09-24-13-32-16.gh-issue-124176.6hmOPz.rst

@@ -0,0 +1,4 @@
+Add support for :func:`dataclasses.dataclass` in
+:func:`unittest.mock.create_autospec`. Now ``create_autospec`` will check
+for potential dataclasses and use :func:`dataclasses.fields` function to
+retrieve the spec information.