test harness: Include $PREBUFFER and $BUFFER in the output.

For human readers' benefit.

Author: danielshahaf

tests/test-highlighting.zsh

@@ -118,6 +118,8 @@ run_test_internal() {
   builtin cd -q -- "$tests_tempdir" || { echo >&2 "Bail out! On ${(qq)1}: cd failed: $?"; return 1 }
 
   echo "# ${1:t:r}"
+  [[ -n $PREBUFFER ]] && printf '# %s\n' "$(typeset_p PREBUFFER)"
+  [[ -n $BUFFER ]] && printf '# %s\n' "$(typeset_p BUFFER)"
 
   # Load the data and prepare checking it.
   local BUFFER CURSOR MARK PENDING PREBUFFER REGION_ACTIVE WIDGET REPLY skip_test unsorted=0