Those are all consumed by our parser, so they all support comments.
I was considering whether they should have a license header at all,
but in the end I decided to add it because those files are often created
by copying parts of real unit files. And if the real ones have a license,
then those might as well. It's easier to add it than to make an exception.
All this test does is manipulate text files in a subdir specified with --testroot.
It can be a normal unittest without the overhead of creating a machine image.
As a bonus, also test the .standalone version.
