Require an operation(Save or Show the results) when testing (#993)

* Require an operation(Save or Show the results) when testing

* using parentheses

tools/test.py

@@ -128,6 +128,10 @@ def parse_args():
 def main():
     args = parse_args()
 
+    assert args.out or args.show, \
+        ('Please specify at least one operation (save or show the results) '
+         'with the argument "--out" or "--show"')
+
     if args.out is not None and not args.out.endswith(('.pkl', '.pickle')):
         raise ValueError('The output file must be a pkl file.')