$ sudo pear install phpunit/PHPUnit
Unknown remote channel: pear.symfony-project.com
phpunit/PHPUnit requires package "channel://pear.symfony-project.com/YAML" (version >= 1.0.2)
phpunit/PHPUnit can optionally use PHP extension "xdebug" (version >= 2.0.5)
No valid packages found
install failed
Que dois-je faire pour pouvoir installer PHPUnit?