Ubuntu 11.10 has had an issue for a while that hasn’t been fixed. This is the only thing that will get phpunit to work with pear. (Outside of using pear you can look up a way to do it without pear. There is an article online about that but I wouldn’t want that kind of burden to do it manually). This is the only thing that worked for me:
sudo apt-get remove phpunit
sudo pear channel-discover pear.phpunit.de
sudo pear channel-discover pear.symfony-project.com
sudo pear channel-discover components.ez.no
sudo pear update-channels
sudo pear upgrade-all
sudo pear install --alldeps phpunit/PHPUnit
sudo pear install --force --alldeps phpunit/PHPUnit