'Only one in-progress rendering should be allowed for a Document'

@mock.patch('kuma.wiki.kumascript.get')
def test_one_render_at_a_time(self, mock_kumascript_get):

    mock_kumascript_get.return_value = (self.rendered_content, None)
    self.d1.render_started_at = datetime.now()
    self.d1.save()
    try:
        self.d1.render('', 'http://testserver/')
        self.fail('An    attempt    to    render    while    another    appears    to    be    in    progress    should    be    disallowed')
    except DocumentRenderingInProgress:
        pass
