PHPUnit 3.4 now supports dependencies between different test methods. It allows you to execute a particular test ONLY IF the test that it depends on executes successfully (using a linked-list class.
He starts off with a simple tests and breaks it up into two different pieces - one to test the creation of the list and another to test the linking of the list. By using the "@depends" notation in the comments of the linking test, you can tell PHPUnit to link the two and only pass if both do. He also touches on Producers and Consumers in testing.