'Send an element from the sink and observe it from the source.'

def test_sendFromSink(self):

    def cb(obj):
        called.append(obj)
    called = []
    self.pipe.source.addObserver('/test[@xmlns="testns"]', cb)
    element = Element(('testns', 'test'))
    self.pipe.sink.send(element)
    self.assertEqual([element], called)
