Entry<Optional<ConsumerGroupState>, Optional<Collection<MemberAssignmentState>>> collectGroupMembers(String groupId, boolean verbose) throws Exception {
            return collectGroupsMembers(Collections.singleton(groupId), verbose).get(groupId);
        }
Returns states of the specified consumer groups and partition assignment states
tools/src/main/java/org/apache/kafka/tools/consumer/group/ConsumerGroupCommand.java