mock: Apply autospec to a mock's return_value

When creating a mock with a class as an autospec:

mock_foo = mock.Mock(autospec=FooClass)

The autospec is only applied to mock_foo itself, and it will
behave as expected. However, the autospec is not applied to its
return_value and thus, the method validation is not enforced:

mock_foo().lish(some_argument_which_doesnt_exist=42)

This patch addresses this issue, and adds necessary unit tests to
test this behaviour.

Change-Id: Icd96beba5a32001cf33f075b801471c6e7c75898
Related-Bug: #1735588

oslotest/mock_fixture.py

@@ -44,13 +44,19 @@ class _AutospecMockMixin(object):
 
     def __init__(self, *args, **kwargs):
         super(_AutospecMockMixin, self).__init__(*args, **kwargs)
-        self.__dict__['_autospec'] = kwargs.get('autospec')
+        autospec = kwargs.get('autospec')
+        self.__dict__['_autospec'] = autospec
         _mock_methods = self.__dict__['_mock_methods']
         if _mock_methods:
             # this will allow us to be able to set _mock_check_sig if
             # the spec_set argument has been given.
             _mock_methods.append('_mock_check_sig')
 
+        # callable mocks with autospecs (e.g.: the given autospec is a class)
+        # should have their return values autospeced as well.
+        if autospec:
+            self.return_value.__dict__['_autospec'] = autospec
+
     def __getattr__(self, name):
         attr = super(_AutospecMockMixin, self).__getattr__(name)
 

oslotest/tests/unit/test_mock_fixture.py

@@ -74,6 +74,7 @@ class MockSanityTestCase(testtools.TestCase):
         for spec in [Foo, Foo()]:
             foo = mock_cls(autospec=spec)
             self._check_autospeced_foo(foo)
+            self._check_autospeced_foo(foo())
 
     def test_mock_autospec_all_members(self):
         self._check_mock_autospec_all_members(mock.Mock)