Add test for assignment of uuid to a deleted BDM

We eventually want to make the BDM uuid column not nullable. This
will require that there are no null values in the column, including in
deleted BDMs. This change adds a test which asserts the online
migration correctly assigns a uuid to soft deleted BDMs.

Part of bp local-disk-serial-numbers

Change-Id: Icf7dd4e3ecf0257d59f82cea80f76f12495594db

nova/tests/unit/objects/test_block_device.py

@@ -429,12 +429,16 @@ class TestBlockDeviceMappingUUIDMigration(test.TestCase):
 
     @staticmethod
     @db_api.pick_context_manager_writer
-    def _create_legacy_bdm(context):
+    def _create_legacy_bdm(context, deleted=False):
         # Create a BDM with no uuid
         values = {'instance_uuid': uuids.instance_uuid}
         bdm_ref = db_models.BlockDeviceMapping()
         bdm_ref.update(values)
         bdm_ref.save(context.session)
+
+        if deleted:
+            bdm_ref.soft_delete(context.session)
+
         return bdm_ref
 
     @mock.patch.object(objects.BlockDeviceMapping, '_create_uuid')
@@ -512,6 +516,10 @@ class TestBlockDeviceMappingUUIDMigration(test.TestCase):
         # Run the online migration again to see nothing was processed
         self._assert_online_migration(0, 0)
 
+        # Assert that we assign a uuid to a deleted bdm.
+        self._create_legacy_bdm(self.context, deleted=True)
+        self._assert_online_migration(1, 1)
+
         # Test that we don't migrate more than the limit
         for i in range(0, 3):
             self._create_legacy_bdm(self.context)