While this is a very nifty bit of code, I'd be very careful about using it for unit testing as there is a high likelihood of minor behavior differences verses a real mongod which can cause surprises in production.

Also, for anyone looking to embed MongoDB and who doesn't mind using C++ it is possible and rather easy. In fact some of our unit tests and all of our tools other than the shell already do this. See https://github.com/mongodb/mongo/blob/master/tools/tool.cpp#... for the details. The DBDirectClient class implements the full C++ driver interface but does all operations in-process. The downside is that unlike when using our drivers (which have no licensing impact on your code) when you embed mongodb within your application it becomes bound by AGPL.

PS- That is really impressive for a weekend project! You should get in touch with us at 10gen if you're looking for a new job.