'L{renderElement} will not write out a doctype if the doctype keyword
argument is L{None}.'

def test_noneDoctype(self):

    element = TestElement()
    d = self.request.notifyFinish()
    def check(_):
        self.assertEqual(''.join(self.request.written), '<p>Hello,    world.</p>')
    d.addCallback(check)
    renderElement(self.request, element, doctype=None)
    return d
