I'm not quite sure what to give feedback on, so I'll just make some general comments and hope they'll help you.
First off; I would love to have PHPUnit test support as this most likely will bring me one step further in the integration of the build process into Jenkins and Sonar.
I currently use Maven to 'build' my Moodle projects with, using the maven-php-plugin.
I say 'build' because obviously there is not really anything to compile, but there are other pieces of the 'build' process that are handled, like code validation, unit testing, reporting (doxygen, phpdocumentor, etc) and archive assembly including deployment docs and jira-issue lists for releases.
As with other setups the unit testing code has it's own directory.
So next to /main/php/moodle directory I have a /test/php/moodle directory containing *Test.php unit test files.
I would expect there to be one moodle unit test class I could extend when needed.
Given the coding style which says no mixed case should be used(*) I guess it would be *test.php files which extend a class called moodle_unit_test_case or something similar.
I understand that using a separate test directory altogether is more complicated when it comes to test code for plugins, but in my view test code has no business being in-between the 'real' code. I would expect people who download Moodle not to get all the test-classes but the tests to be available separately.
(*) I'm still not sure why mixed case is not used and find it to be one of the major challenges when writing Moodle code.