public static Map<String, String> topicConfig(String topic) {
        return ALL_TOPICS.getOrDefault(topic, new ConcurrentHashMap<>());
    }
get topic config stored in allTopics.
@param topic name of topic
@return topic configurations.
connect/mirror/src/test/java/org/apache/kafka/connect/mirror/clients/admin/FakeLocalMetadataStore.java