#4 fixed the positions edit page throws 500

Fixed the positions edit page problem.
Added test.
![zrzut ekranu z 2014-08-11 11 45 26](https://cloud.githubusercontent.com/assets/6718923/3874082/3823011a-213c-11e4-90dc-7cdc8f7250ed.png)

don't ever use `to_not raise_error`, it doesn't test anything. check the expected value.