add unittest for moving around the marks

Change-Id: I31849e655ab9e9c9acc62f1fdc124d40342deb49
Reviewed-on: https://gerrit.libreoffice.org/9069
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>