public boolean registerAdminExt(final String group, final MQAdminExtInner admin) {
        if (null == group || null == admin) {
            return false;
        }

        MQAdminExtInner prev = this.adminExtTable.putIfAbsent(group, admin);
        if (prev != null) {
            log.warn("the admin group[{}] exist already.", group);
            return false;
        }

        return true;
    }
@Test
    public void testRegisterAdminExt() {
        boolean flag = mqClientInstance.registerAdminExt(group, mock(MQAdminExtInner.class));
        assertThat(flag).isTrue();

        flag = mqClientInstance.registerAdminExt(group, mock(MQAdminExtInner.class));
        assertThat(flag).isFalse();

        mqClientInstance.unregisterAdminExt(group);
        flag = mqClientInstance.registerAdminExt(group, mock(MQAdminExtInner.class));
        assertThat(flag).isTrue();
    }