gnulib tests leftovers

[Ralf Wildenhues]

Hello,

taking a tree from
  gnulib-tool --with-tests --test

and running distcheck on it ends with

[...]
| rm -f Makefile
| ERROR: files left in build directory after distclean:
| ./gltests/out
| make[1]: *** [distcleancheck] Error 1
| make[1]: Leaving directory `/tmp/build/dummy-0/_build'
| make: *** [distcheck] Error 1

A quick git grep reveals the following tests as candidates:

tests/test-verify.sh
tests/test-xalloc-die.sh
tests/test-xstrtoimax.sh
tests/test-xstrtol.sh
tests/test-xstrtoll.sh
tests/test-xstrtoumax.sh

Now, I'm not intricate with the current gnulib test framework, and I
wonder why 'err' is not a leftover file.  Which is the preferred way to
remove files here?  Supply a custom cleanup_ function?  Put temp files
in $test_dir_?

Are the tests supposed to be usable with the parallel-tests framework?
In that case, 'out' and 'err' are not sufficiently unique as names for
concurrent tests.  (Yes, I noted that some tests ask for a password, and
won't work with this either for use of stdin, but a majority of gnulib
users may not use these tests.)

Thanks,
Ralf