public String quorumVotersConfig() throws ExecutionException, InterruptedException {
        Collection<Node> controllerNodes = QuorumConfig.voterConnectionsToNodes(
            controllerQuorumVotersFutureManager.future.get()
        );
        StringBuilder bld = new StringBuilder();
        String prefix = "";
        for (Node node : controllerNodes) {
            bld.append(prefix).append(node.id()).append('@');
            bld.append(node.host()).append(":").append(node.port());
            prefix = ",";
        }
        return bld.toString();
    }
Wait for a controller to mark all the brokers as ready (registered and unfenced).
And also wait for the metadata cache up-to-date in each broker server.
core/src/test/java/kafka/testkit/KafkaClusterTestKit.java