Duplicate dom templates

```
11:26 PM <wycats_> can someone do me a huge favor?
11:27 PM <wycats_> I want a PR that throws if you have the same template in DOM multiple times
11:27 PM <wycats_> application is a huge culprit
11:27 PM <wycats_> basically exception instead of "last one wins"
```

Opening for discussion.

- [ ] Rename tests descriptions