RED-21827, Fix bug in pipeline: watch command would fail on hashmaps key (#1)

Author: gildaf

mockredis/pipeline.py

@@ -39,6 +39,8 @@ def watch(self, *keys):
             raise RedisError("Cannot issue a WATCH after a MULTI")
         self.watching = True
         for key in keys:
+            if key in self._watched_keys:
+                continue
             self._watched_keys[key] = deepcopy(self.mock_redis.redis.get(self.mock_redis._encode(key)))  # noqa
 
     def multi(self):