You must install PHPUnit to use the CakePHP(tm) Test Suite.
PHPUnit can be installed with pear, using the pear installer.
To install with the PEAR installer run the following commands:
pear channel-discover pear.phpunit.depear channel-discover components.ez.nopear channel-discover pear.symfony-project.compear install phpunit/PHPUnit-3.6.4Once PHPUnit is installed make sure its located on PHP's include_path by checking your php.ini
For full instructions on how to install PHPUnit, see the PHPUnit installation guide.