I would like to downgrade my installation of PHPUnit 3.4 to 3.3. I'm just not sure how to do it.
How do I install version 3.3 of PHPUnit on Ubuntu using PEAR?
You need to know the exact version number you wish to downgrade to. At the time of writing, the last release you're after is 3.3.17, which can be found out by checking the appropriate PEAR channel.
To downgrade to that particular version execute two commands:
pear uninstall phpunit/PHPUnit
pear install phpunit/PHPUnit-3.3.17