Tests, for each installed plugin, if the plugin structure seems correct.
This is very useful if you have many external plugins that are updated frequently through SVN; sometimes the repositories move and you get an invalid structure (for example, the author starts to use branches).
If you think this plugin is useless - well, I do too. You shouldn't use externals, it's too unreliable for production.
Optional, as you can just run the PHP file.
ln -s ../../plugins/sfPluginsTestPlugin/test/unit/pluginsTest.php test/unit/pluginsTest.php
You can also just copy the file to your test/unit directory, but you will have to edit the "include" line. You might want to edit the file to customize it anyway.
php symfony test-unit plugins