$AT_OUTPUTdirectory are sent back to CodeGrade so the student and/or teacher can review them later on.
$AT_OUTPUTdirectory is cleared between each AutoTest category.
$AT_OUTPUTdirectory is writable by the user running the AutoTest steps. This means that students will also be able to write to this directory, or even overwrite files that were generated earlier. To prevent this from happening, see the Limiting Student Access chapter in AutoTest Setup.