I have had to de- and reinstall a newer version of PHPUnit following these directions. Now when I\'m launching this line
sudo pear install --alldeps phpunit/PHPU
Following Plínio César, I solved it finally, but with slight variation:
First I did a "sudo apt-get remove phpunit" to remove the faulty installation. Then using pear to do the phpunit installation:
sudo pear install pear.symfony.com/Yaml
sudo pear channel-discover pear.phpunit.de
sudo pear config-set auto_discover 1
sudo pear install --alldeps pear.phpunit.de/PHPUnit
Thanks Plinio Cesar!!!