public Builder setPerServerProperties(Map<Integer, Map<String, String>> perServerProperties) {
            this.perServerProperties = Collections.unmodifiableMap(
                    perServerProperties.entrySet().stream()
                            .collect(Collectors.toMap(Map.Entry::getKey, e -> Collections.unmodifiableMap(new HashMap<>(e.getValue())))));
            return this;
        }
Represents an immutable requested configuration of a Kafka cluster for integration testing.
core/src/test/java/kafka/test/ClusterConfig.java