On the Zumba Engineering blog, Chris Saylor has a post announcing the open sourcing of mongounit, a PHPUnit extension useful for doing database testing directly on MongoDB databases - Mongounit.
One of our more recent projects has given the team exposure to MongoDB. As such, we needed an easy way to test the models that utilize mongo in a similar fashion to how we test models that talk to mysql. Using this framework, it's easy to implement mongo test cases to easily create fixture data in collections, or simply clear collections between test cases.
You can find the latest release of this tool on github and see an example testcase here.