Remove hard coded Ids

Hi I have tried to update the tests to they don't use hardcoded ids. After I did pub update I got some issues with running the tests about relationshipProperties. Since I haven't changed anything from them, I am not sure what happened. 

To run the test file in WebStorm I had to add it to a library. The unittest library also complained about some calls to ```expect()``` that were outside of a ```test()``` so I commented those out.

Can you run the tests successfully after these changes?

This is my first try with dart so if you see something strange, let me know :)

regards Oskar