Unforunately, the MockJspWriter throws a NotImplementedException when any of the Writer methods are invoked and
as you might guess, Velocity uses the Writer methods. I'velocityEngine subclassed the MockJspWriter for the time being so
that we can do testing on the results until MockJspWriter gets fully implemented.
todo replace this once MockJspWriter implements Writer correctly (i.e. doesn't throw NotImplementException)