def test_render(self):
        args = []
        preproc = object()
        class DocFactory(object):
            def load(self, ctx, preprocessors, precompile=None):
                args.append(preprocessors)
                return "result"

        element = Element()
        element.preprocessors = (preproc,)
        element.docFactory = DocFactory()
        self.assertEqual(element.render(None), "result")
        self.assertEqual(args, [(preproc,)])
L{Element.render} loads a document from the C{docFactory} attribute and
dataset/ETHPy150Open twisted/nevow/nevow/test/test_element.py/ElementTests.test_render