function add_suffix () {
  base_s="$1"
  if [ -e "${base_s}" ]; then

    # we could rename the existing but let's just leave things as is.
    # echo "${base_s} already exists."
    #if [ -e "${base_s}_1" ]; then
    #  echo "ERROR: ${base_s}_1 already exists. Unexpected." >&2
    #else
    #  # we are renaming the *existing* dir.
    #  echo "Suffixing '_1' to existing dir name ({base_s})."
    #  sudo mv "${base_s}" "${base_s}_1"
    #fi

    # The non-suffixed dir should be interpreted as number 1.
    suffix=2
    while [ -e "${base_s}_${suffix}" ]; do
      suffix=$((suffix + 1))
    done
    base_s="${base_s}_${suffix}"
  fi
  echo "${base_s}"
}

# "Missing glyphs" from Noto Tibetan:
# supported-languages_polyglossia_pdf4_systemF
#
# %28APA%29,_v._6: not sure why these are failing (the apa6.cls exists) but not worth the time since obsolete.
#
# supported-languages_polyglossia_.*_systemF: The LuaTeX changes started failing at 99299169. I think XeTeX failed before. I need to figure out the Noto fonts thing.
#
# Europe_CV: see here: https://github.com/gsilano/EuropeCV/issues/29
# There is a patch but is not backwards-compatible so it's not clear if
# it will be merged.
#
# BATCH_compare-test: I'm not sure why this fails, but no time to look into it.
#
# BATCH_vcs-info, BATCH_outline-beamer: these tests fail when configure.ac has, e.g., "beta".
#   We know what we need to do to fix this, but just need to do it.
#   sk: see personal email here for more info:
#     Message-ID:<20221221165514.pbfrlpt77o3my55o@gary>
#
# Astronomical: the required file aastex62.cls is not found anymore. Probably there is a new version with a new file name.
#               TODO: look into ^this when I have time.
#               Jean-Pierre helped transition things to a new class (and file name) version.
#
ctest_exclude='(supported-languages_polyglossia_.*_systemF|(%28APA%29,_v._6|Astronomical).*(pdf|dvi|lyx22|lyx23)|BATCH_compare-test|BATCH_outline-beamer|BATCH_vcs-info)'
# timeout of 10m.
function ctest-reg-if-fail ()
{
  ctest -E "${ctest_exclude}" --timeout 600 $@
  ret="$?"

  failed_log="Testing/Temporary/LastTestsFailed.log"
  # there is no file if no failures.
  if [ -e "${failed_log}" ]; then
    if [ -e "/tmp/LastTestsFailed" ]; then
      target_f="$( add_suffix "/tmp/LastTestsFailed" )"
      # we want the root one to be the newest.
      mv /tmp/LastTestsFailed "${target_f}"
    fi
    cp -f "${failed_log}" /tmp/LastTestsFailed
  fi

  return "${ret}"
}
# This tests all of the ones excluded above. Good to check once in a while to
# see if we can "uninvert" them (in our 'ctest_exclude' variable that is).
alias ctest-reg-if-fail-INVERTED='ctest -R "${ctest_exclude}"'
# TODO: this doesn't work. Ask on SO? Use my specific case (of ctest)
source /usr/share/bash-completion/completions/ctest
complete -F _ctest ctest-reg-if-fail
#
# useful when want to test mainly for polyglossia regressions
alias ctest-reg-if-fail-polyglossia='ctest -E "${ctest_exclude}" -R "systemF" --timeout 600'