BUG: Fix handling empty migration list for VMs

lib/apis/openstack_api/openstack_server.py

@@ -157,7 +157,13 @@ def wait_for_migration_status(
     """
     start_time = time.time()
     while time.time() - start_time < timeout:
-        migration = next(conn.compute.migrations(instance_uuid=server_id))
+        try:
+            migration = next(conn.compute.migrations(instance_uuid=server_id))
+        except StopIteration:
+            logger.info("No migration details available for %s yet", server_id)
+            time.sleep(interval)
+            continue
+
         logger.info("Status of migration of server %s: %s", server_id, migration.status)
         if migration.status == status:
             return migration

tests/lib/apis/openstack_api/test_openstack_server.py

@@ -659,3 +659,17 @@ def test_shutoff_server_propagates_resource_failure():
         shutoff_server(mock_conn, "server-123")
 
     assert exc_info.value is expected_exception
+
+
+def test_with_empty_migration_list():
+    """
+    Tests that the code can handle an empty list of migrations e.g. when we
+    ask before nova gets the message we're migrating
+    """
+    mock_conn = MagicMock()
+    mock_conn.compute.migrations.side_effect = []  # Return nothing intentionally
+
+    with pytest.raises(ResourceTimeout):
+        wait_for_migration_status(
+            mock_conn, "test-server-id", "should-timeout", interval=1, timeout=1
+        )