Add tests for migration code

[davidbanham]

No description provided.

[s-taylor]

I was thinking about this and wondering if migrations should be a separate node module? I think any instances where a developer is unlikely to ever want to or need to change the code, it would be better separated. This also then reduces the clutter in redbeard when running generators and means as a developer you're not running migration tests every time you run your tests for code that you're never going to change.

Also rethinkdb-migrator might be a good open source candidate?