hello,
hum really sorry for the delay of my answer.
Don't think I had the notification.
Anyway, please accept my apologies.
Shell_tester.php is a file requires by simpletest unit test cases.
You really need it only if you wants to test unit test cases. Ok it's requires.
I'll update my simpletest package and in other case you can download it here:
simpletest.org/
best regards