Under the options you can turn Friendly Hits ON. Start a two player game and hit your co-op partner until they need to be revived/reanimated tapping when a counter appears. I find this best to do if you start up midway through Stage One (Shopping District). There, no one will attack if you stay to the left. Again, killing your teammate will take time if you aren't leveled up enough so best to wait until everything else is done.
If playing multiplayer this will occur many times naturally. Reanimating your teammate may not always be the best option though, keep in mind. Often it will get you killed and there's no use having everyone dead.