'Test adding duplicate features to disco#info.'

def testFeaturesDuplicate(self):

    iq = self.Iq()
    iq['disco_info'].add_feature('foo')
    iq['disco_info'].add_feature('bar')
    iq['disco_info'].add_feature('foo')
    self.check(iq, '\n                                        <iq>\n                                                <query    xmlns="http://jabber.org/protocol/disco#info">\n                                                        <feature    var="foo"    />\n                                                        <feature    var="bar"    />\n                                                </query>\n                                        </iq>\n                                ')
