Allow rules to correct commands that time out

tests/utils.py

@@ -10,7 +10,8 @@ def Rule(name='', match=lambda *_: True,
          get_new_command=lambda *_: '',
          enabled_by_default=True,
          side_effect=None,
-         priority=DEFAULT_PRIORITY):
+         priority=DEFAULT_PRIORITY,
+         requires_output=True):
     return types.Rule(name, match, get_new_command,
                       enabled_by_default, side_effect,
-                      priority)
+                      priority, requires_output)