def test_listMethods(self):
        """
        A subclass of L{XMLRPC} can override C{listProcedures} to define
        Overriding listProcedures should prevent introspection from being
        broken.
        """
        resource = TestListProcedures()
        addIntrospection(resource)
        self.createServer(resource)
        d = self.proxy.callRemote("system.listMethods")
        def listed(procedures):
            # The list will also include other introspection procedures added by
            # addIntrospection.  We just want to see "foo" from our customized
            # listProcedures.
            self.assertIn('foo', procedures)
        d.addCallback(listed)
        return d

        A subclass of L{XMLRPC} can override C{listProcedures} to define
        Overriding listProcedures should prevent introspection from being
        broken.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_xmlrpc.py