Good open source projects with Rails4, Mongoid and RSpec

for learning purpose I'm searching for good open source projects with Mongoid and RSpec. I'm developing with mongoid now for over a year and I'm coming to the point, where the whole design of the application and its tests are getting slower and slower (but, luckily, still stable).

That means, I have a lot of models that depend on each other, APIs that depend on the models and so on. And it seems to me, that this makes the whole test suite slow.

I caught myself creating a lots of objects in the database, to have a valid instance of a model (which has a presence: true on 3 other models, which in turn have also a presence: true on other models, and so on), just to test one unit case, and this seems like a huge overkill.

I know about spies, stubbing and mocks, but I thought, I could have a look into other, good open source projects to learn from them. I already found some similar posts, but most of them are back from 2010 or 2011 and they seem outdated.

I also read blog posts about testing, http://betterspecs.org/, best practises and so on. But I would like to see the whole stuff playing together in a good tested and well designed open source project.

I would also appreciate projects with MySQL or Postgresql. And if anybody can recommend good books, let me know!

thx in advance!