sudo mkdir /usr/local/temp;
sudo chmod -R 777 /usr/local/temp;
sudo mkdir /usr/local/share/pear;
sudo chmod -R 777 /usr/local/share/pear;
curl http://pear.php.net/go-pear | sudo php;

Set /usr/local as path prefix and install.

You should then be able to use pear, e.g.: pear help.

In order to install modules you also need a temp dir:

sudo mkdir /usr/local/temp;
sudo chmod 0777 /usr/local/temp/;

You can now install PHPUnit:

sudo pear channel-discover pear.phpunit.de;
sudo pear install phpunit/PHPUnit;

Have Fun!