FYI. Usually I get 53 passed tests, but occasionally (~ once / month), I
get 52 passes and one failure. I cannot boost the verbosity because the
race condition is not repeatable. Here is the failure; when I re-ran the
tests, I got 53 passes.

Test ../../../src/zsh-2019-12-01/Test/C02cond.ztst failed: bad status 1,
expected 0 from:
  if [[ ${mtab::="$({mount || /sbin/mount || /usr/sbin/mount}
2>/dev/null)"} = *[(]?*[)] ]]; then
    print -u $ZTST_fd 'This test takes two seconds...'
  else
    unmodified_ls="$(ls -lu $unmodified)"
    print -u $ZTST_fd 'This test takes up to 60 seconds...'
  fi
  sleep 2
  touch $newnewnew
  if [[ $OSTYPE == "cygwin" ]]; then
    ZTST_skip="[[ -N file ]] not supported on Cygwin"
  elif (( isnfs )); then
    ZTST_skip="[[ -N file ]] not supported with NFS"
  elif { (( ! $+unmodified_ls )) &&
         cat $unmodified &&
         { df -k -- ${$(print -r -- "$mtab" |
                        awk '/noatime/ {print $1,$3}'):-""} | tr -s ' ' |
           fgrep -- "$(df -k . | tail -1 | tr -s ' ')" } >&/dev/null } ||
       { (( $+unmodified_ls )) && SECONDS=0 &&
         ! until (( SECONDS >= 58 )); do
             ZTST_hashmark; sleep 2; cat $unmodified
             [[ $unmodified_ls != "$(ls -lu $unmodified)" ]] && break
 done }; then
    ZTST_skip="[[ -N file ]] not supported with noatime file system"
  else
    [[ -N $newnewnew && ! -N $unmodified ]]
  fi
Was testing: -N cond
../../../src/zsh-2019-12-01/Test/C02cond.ztst: test failed.
The following may (or may not) help identifying the cause:
  This test can fail on NFS-mounted filesystems as the access and
  modification times are not updated separately.  The test will fail
  on HFS+ (Apple Mac OS X default) filesystems because access times
  are not recorded.  Also, Linux ext3 filesystems may be mounted
  with the noatime option which does not update access times.
  Failures in these cases do not indicate a problem in the shell.
../../../src/zsh-2019-12-01/Test/C03traps.ztst: starting.
This test takes at least three seconds...
This test, too, takes at least three seconds...
Another test that takes three seconds
../../../src/zsh-2019-12-01/Test/C03traps.ztst: all tests successful.

  - Vin