bpo-45756: do not execute @property descrs while creating mock autospecs

Lib/unittest/mock.py

@@ -494,6 +494,10 @@ def _mock_add_spec(self, spec, spec_set, _spec_as_instance=False,
         _spec_asyncs = []
 
         for attr in dir(spec):
+            if isinstance(inspect.getattr_static(spec, attr, None), property):
+                # Don't execute `property` decorators with `getattr`.
+                # It might affect user's code in unknown way.
+                continue
             if iscoroutinefunction(getattr(spec, attr, None)):
                 _spec_asyncs.append(attr)
 

Lib/unittest/test/testmock/testmock.py

@@ -896,6 +896,36 @@ def set_attr():
         self.assertRaises(AttributeError, set_attr)
 
 
+    def test_class_with_property(self):
+        class X:
+            @property
+            def some(self):
+                raise ValueError('Should not be raised')
+
+        mock = Mock(spec=X)
+        self.assertIsInstance(mock, X)
+
+        mock = Mock(spec=X())
+        self.assertIsInstance(mock, X)
+
+
+    def test_class_with_settable_property(self):
+        class X:
+            @property
+            def some(self):
+                raise ValueError('Should not be raised')
+
+            @some.setter
+            def some(self, value):
+                raise TypeError('Should not be raised')
+
+        mock = Mock(spec=X)
+        self.assertIsInstance(mock, X)
+
+        mock = Mock(spec=X())
+        self.assertIsInstance(mock, X)
+
+
     def test_copy(self):
         current = sys.getrecursionlimit()
         self.addCleanup(sys.setrecursionlimit, current)

Misc/NEWS.d/next/Library/2021-12-03-11-19-44.bpo-45756.nSDJWj.rst

@@ -0,0 +1,2 @@
+Do not execute ``@property`` descriptors while creating autospecs in :mod:`unittest.mock`.
+This was not safe and could affect users' code in unknown way.