On the Zubma Engineering blog today Chris Saylor has written up a tutorial showing how they used traits to use multiple data sources with Mongounit, working around the single source limitations it enforces.
A while back we open sourced Mongounit, a PHPUnit extension for testing models utilizing mongodb. One key issue that we've discovered as we incorporate MongoDB into more of our data models is that extending Mongounit's TestCase class limits that unit test towards Mongo only as the datasource. Since only a portion of our data is in Mongo while the remaining is in MySQL, limiting a test case to work with one datasource or another is too limiting.
They tried two other solutions first, separating out the tests by data source and manually clear the Mongo data in the tests, but both ran into problems. Instead, they opted to use traits to provide drop-in Mongo testing support as needed. It provides a simple interface to set up and tear down the needed Mongo resources - an example of which is also provided in the post. The code for the trait can be found on Github.