Add a reset for traits DB sync

Some functional tests were failing, due to standard traits not being
found. The cause was that there is a flag that ensures that these
standard traits are only loaded once from the os_traits module to the
DB. The test fixtures, though, would clean up the DB between runs, and
the traits would never be re-loaded. This patch fixes that by directly
resetting this flag in the base test code.

Closes-bug: #1701035

Change-Id: I5dc0220310986c5b9fe5b71013c573c3d98cb9aa

nova/test.py

@@ -294,6 +294,9 @@ class TestCase(testtools.TestCase):
         # caching of that value.
         utils._IS_NEUTRON = None
 
+        # Reset the traits sync flag
+        objects.resource_provider._TRAITS_SYNCED = False
+
         mox_fixture = self.useFixture(moxstubout.MoxStubout())
         self.mox = mox_fixture.mox
         self.stubs = mox_fixture.stubs

nova/tests/unit/objects/test_resource_provider.py

@@ -13,6 +13,7 @@
 import mock
 import six
 
+import nova
 from nova import context
 from nova import exception
 from nova import objects
@@ -581,3 +582,14 @@ class TestResourceClass(test.NoDBTestCase):
         rc = objects.ResourceClass(self.context)
         exc = self.assertRaises(exception.ObjectActionError, rc.create)
         self.assertIn('name is required', str(exc))
+
+
+class TestTraitSync(test_objects._LocalTest):
+    @mock.patch("nova.objects.resource_provider._trait_sync")
+    def test_sync_flag(self, mock_sync):
+        synced = nova.objects.resource_provider._TRAITS_SYNCED
+        self.assertFalse(synced)
+        # Sync the traits
+        nova.objects.resource_provider._ensure_trait_sync(self.context)
+        synced = nova.objects.resource_provider._TRAITS_SYNCED
+        self.assertTrue(synced)