I just uploaded a new update to my PipelineTesting library. This one comes courtesy of Gregory Van de Wiele, who kindly made me aware of a nasty bug: The library wasn't handling schemas with no targetNamespace correctly when adding them to the pipeline context.
Because of this, you needed to specify the documentSpec name as "#root" instead of simply "root". This has now been fixed in this version and I added a new unit test to make sure it doesn't come up again. Thanks a lot Gregory!
As usual you can download the updated code/binaries from here.