test harness: Tweak quiet-test output

- Print the test name and data after the plan line

- Split on the plan line rather than on comments

  + That makes tap-filter more suitable to filter TAP output generated by other
    TAP producers.

  + However, the filtered output deletes the plan line and adds a blank line in
    its stead.  This suits our use-case of interactive test runs.

tests/tap-filter

@@ -41,5 +41,7 @@ use strict;
 undef $/; # slurp mode
 print for
   grep { /^ok.*# TODO/m or /^not ok(?!.*# TODO)/m or /^Bail out!/m }
-    split /^(?=#)/m,
+    # Split on plan lines and remove them from the output.  (To keep them,
+    # use the lookahead syntax, «(?=…)», to make the match zero-length.)
+    split /^\d+\.\.\d+$/m,
       <STDIN>;

tests/test-highlighting.zsh

@@ -117,10 +117,6 @@ run_test_internal() {
   local srcdir="$PWD"
   builtin cd -q -- "$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
   local expected_mismatch
@@ -145,7 +141,12 @@ run_test_internal() {
     expected_region_highlight=("${(@n)expected_region_highlight}")
   fi
 
+  # Print the plan line, and some comments for human readers
   echo "1..$(( $#expected_region_highlight + 1))"
+  echo "## ${1:t:r}"
+  [[ -n $PREBUFFER ]] && printf '# %s\n' "$(typeset_p PREBUFFER)"
+  [[ -n $BUFFER ]] && printf '# %s\n' "$(typeset_p BUFFER)"
+
   local i
   for ((i=1; i<=$#expected_region_highlight; i++)); do
     local -a expected_highlight_zone; expected_highlight_zone=( ${(z)expected_region_highlight[i]} )