触发器问题

今天学习5.0的触发器，有个问题想请教。

DROP TABLE IF EXISTS `system`.`test`;
CREATE TABLE `system`.`test` (
`testId` int(10) unsigned NOT NULL auto_increment,
`TEST_TIME` datetime default NULL,
`TEST_name` varchar(30) default NULL,
`huffmanCode` text NOT NULL,
`LchildCount` int(10) unsigned NOT NULL,
`RchildCount` varchar(45) NOT NULL,
PRIMARY KEY (`testId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TRIGGER test_Children_count
BEFORE INSERT ON test
FOR EACH ROW
UPDATE test SET TEST_name='1' WHERE `testid`<>NEW.`testid`;
插入一条数据以后，出现错无提示:

Can't update table 'test' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
能告诉我这是什么原因吗？！