diff --git a/tools/test.py b/tools/test.py
index 61004d8c187..308675b5ccf 100644
--- a/tools/test.py
+++ b/tools/test.py
@@ -108,7 +108,8 @@ def merge_args(cfg, args):
             'The dump file must be a pkl file.'
         dump_metric = dict(type='DumpResults', out_file_path=args.dump)
         if isinstance(cfg.test_evaluator, (list, tuple)):
-            cfg.test_evaluator = list(cfg.test_evaluator).append(dump_metric)
+            cfg.test_evaluator = list(cfg.test_evaluator)
+            cfg.test_evaluator.append(dump_metric)
         else:
             cfg.test_evaluator = [cfg.test_evaluator, dump_metric]