Don't report deleted attributes in __dir__ (GH#10148)

When an attribute is deleted from a Mock, a sentinel is added rather
than just deleting the attribute. This commit checks for such sentinels
when returning the child mocks in the __dir__ method as users won't
expect deleted attributes to appear when performing dir(mock).

Lib/unittest/mock.py

@@ -684,12 +684,14 @@ class NonCallableMock(Base):
         extras = self._mock_methods or []
         from_type = dir(type(self))
         from_dict = list(self.__dict__)
+        from_child_mocks = [
+            m_name for m_name, m_value in self._mock_children.items()
+            if m_value is not _deleted]
 
         from_type = [e for e in from_type if not e.startswith('_')]
         from_dict = [e for e in from_dict if not e.startswith('_') or
                      _is_magic(e)]
-        return sorted(set(extras + from_type + from_dict +
+        return sorted(set(extras + from_type + from_dict + from_child_mocks))
-                          list(self._mock_children)))
 
 
     def __setattr__(self, name, value):

Lib/unittest/test/testmock/testmock.py

@@ -885,6 +885,15 @@ class MockTest(unittest.TestCase):
             patcher.stop()
 
 
+    def test_dir_does_not_include_deleted_attributes(self):
+        mock = Mock()
+        mock.child.return_value = 1
+
+        self.assertIn('child', dir(mock))
+        del mock.child
+        self.assertNotIn('child', dir(mock))
+
+
     def test_configure_mock(self):
         mock = Mock(foo='bar')
         self.assertEqual(mock.foo, 'bar')

Misc/NEWS.d/next/Library/2018-10-27-11-54-12.bpo-35082.HDj1nr.rst

@@ -0,0 +1,2 @@
+Don't return deleted attributes when calling dir on a
+:class:`unittest.mock.Mock`.