If you have a slightly dated PHPUnit test-case suite, and like me, have recently reinstalled your OS you will likely be running a modern version of PHPUnit (3.5/3.6).
Keeping up with changes to PHPUnit's suite of extensions can be occasionally dizzying, things have been put in and then ripped out of the core quite frequently in the last few releases. A common problem I'm seeing lately upgrading my test-suites to be 3.6 compatible, is the extraction of database testing classes to their own package on the pear.phpunit.de channel.
If you see an error like this:
> include(PHPUnit/Extensions/Database/TestCase.php): failed to open stream: No such file or directory
Odds are you need to do this:
$ sudo pear config-set auto_discover 1 $ sudo pear install --alldeps pear.phpunit.de/DbUnit