If your going to use a computer to generate evidence then yes you must allow the defence to look at the technique that means source code. You must never be required to merely observe at somebody else's lab especially when there companys continued business relies on the test succeeding. Realy anything that another lab that is not associated to the first can not do should not be admissible.
This gets even more important when the tests are destructive so it can only be done once. Validating the means used etc etc elsewise it becomes a black box to provide evidence against whoever they want.