Install PHPUnit through Pear, MacPorts, or whatever system you use. It is available for many packaging systems. When done, you should be able to run "phpunit" from your command line and get a help response.
Or download it.
Link to an existing installation of concrete5 (*), e.g.:
cd concrete5-tests
ln -s /Library/WebServer/WebSites/c541/web/ ./web
(*) Do NOT link to a production version because it's possible some files or database values may be modified. You can download the latest development version from http://github.com/concrete5/concrete5/ and create the link as described above, but you must go through the c5 install routines before testing.
phpunit --bootstrap tests/bootstrap.php tests
Expected output is something like
PHPUnit 3.5.13 by Sebastian Bergmann.
.............
Time: 0 seconds, Memory: 15.25Mb
OK (13 tests, 128 assertions)
Send us tests via pull request, or send @aembler a private message if you'd like direct commit access to this repository.