twitter/scalding — pull request #759 by daisyzhou (2014-01-27 20:14:22+00:00)
Title: "Require" sources in JobTests to have a mock buffer.

This is just adding an error message to inform users writing JobTests that they need to
provide buffers for every source used in the job.

We see a lot of users get confused by a "Key not found" exception if the sources in their JobTest aren't exactly equal.