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

def test_sendFromSource(self):

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