Composer global

$ composer global require phpunit/phpunit
$ composer global require phpunit/dbunit
$ composer global require phing/phing
$ composer global require phpdocumentor/phpdocumentor
$ composer global require sebastian/phpcpd
$ composer global require phploc/phploc
$ composer global require phpmd/phpmd
$ composer global require squizlabs/php_codesniffer
This will install PHPUnit and all its dependencies into the ~/.composer/vendor/ directory and, most importantly, the phpunit CLI tools are installed into ~/.composer/vendor/bin/.

Simply add this directory to your PATH in your ~/.bash_profile (or ~/.bashrc) like this:

export PATH=~/.composer/vendor/bin:$PATH
and phpunit is now available on your command line.

To keep your tools up to date, you simply do this:

composer global update
To remove a package, you edit ~/.composer/composer.json and then run composer global update.