title: PHPunit will only run the last descendant of a testsuite
body: <p>Basically some of my test classes extend other test classes. For example I have a DocumentTest class and a DiffableTest that extends from it.</p>
  
  <p>When I run phpunit on the directory they are in, it will only test the DiffableTest class and ignore the DocumentTest one. How do I make sure that both suites are being called?</p>