--pear channel-discover pear.phpunit.de
--pear install phpunit/PHPUnit
此时会显示：
No valid packages found
install failed
(安装phpunit失败，此时通过pear upgrade pear更新pear后继续安装)
--pear upgrade pear
--pear info pear
--pear channel-discover pear.phpunit.de
--pear install phpunit/PHPUnit
至此完成，最终显示：
install ok: channel://pear.phpunit.de/PHPUnit-3.4.13