tests: Allow marking the cardinality check as TODO (XFail).

Needed for next commit.

tests/README.md

@@ -21,6 +21,11 @@ with the provided string as the reason.
 If a test sets `unsorted=1` the order of highlights in `$expected_region_highlight`
 need not match the order in `$region_highlight`.
 
+Normally, tests fail if `$expected_region_highlight` and `$region_highlight`
+have different numbers of elements.  Tests may set `$expected_mismatch` to an
+explanation string (like `$todo`) to avoid this and mark the cardinality check
+as todo.
+
 **Note**: `$region_highlight` uses the same `"$i $j $style"` syntax but
 interprets the indexes differently.
 

tests/test-highlighting.zsh

@@ -98,6 +98,7 @@ run_test_internal() {
 
   # Load the data and prepare checking it.
   local BUFFER CURSOR MARK PENDING PREBUFFER REGION_ACTIVE WIDGET skip_test unsorted=0
+  local expected_mismatch
   local -a expected_region_highlight region_highlight
   . "$srcdir"/"$1"
 
@@ -154,7 +155,7 @@ run_test_internal() {
   if (( $#expected_region_highlight == $#region_highlight )); then
     print -r -- "ok $i - cardinality check"
   else
-    print -r -- "not ok $i - have $#expected_region_highlight expectations and $#region_highlight region_highlight entries"
+    print -r -- "not ok $i - have $#expected_region_highlight expectations and $#region_highlight region_highlight entries: «$(typeset -p expected_region_highlight)» «$(typeset -p region_highlight)»" "${expected_mismatch:+" # TODO : $expected_mismatch"}"
   fi
 }