This is a follow-up to 4967d498 and
avoids to have setup errors making these tests silently pass.

Also cleanup code a bit & share common init sequence.

Change-Id: I043447a28f5e2c9f416aa906135030c07b2cacc8
Reviewed-on: https://gerrit.libreoffice.org/63800
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>