One of the ways to install PHPUnit is through PHP Pear. You must already have PHP Pear installed. This is verified to work on Mac OS X Snow Leopard.
To install PHPUnit through PHP PEAR, the following channels have to be added before an install:
pear channel-discover pear.phpunit.de pear channel-discover pear.symfony-project.com pear channel-discover components.ez.no pear install phpunit/PHPUnit
You should see the following response:
PHPUnit 3.5.0 by Sebastian Bergmann.