mutable.Buffer does not work with Scalding JobTest for Type Safe API
So, while I don't have a great answer to this post, I have what worked for me. Basically my problem was that I was using ScalaTest to run my Scalding jobs from this link: Using the ScalaTest Maven plugin. This worked fine for my unit tests on operations but this caused weirdness when using ScalaTest with JobTest. After talked to the Scalding devs and finally acknowledging my team's own success with JUnitRunner, I decided to go with that. I changed my POM to support JUnitRunner and added @RunWith(classOf[JUnitRunner]) annotations to my tests. Everything worked and behaved like I wanted them too.