gettext tests: don't ignore "test-tool regex" exit code

Amend a prerequisite check added in 5c1ebcc (grep/icase: avoid
kwsset on literal non-ascii strings, 2016-06-25) to do invoke
'test-tool regex' in such a way that we'll notice if it dies under
SANITIZE=leak due to having a memory leak, as opposed to us not having
the "ICASE" support we're checking for.

Because we weren't making a distinction between the two I'd marked
these tests as passing under SANITIZE=leak in 03d85e2 (leak tests:
mark remaining leak-free tests as such, 2021-12-17).

Doing this is tricky. Ideally "test_lazy_prereq" would materialize as
a "real" test that we could check the exit code of with the same
signal matching that "test_must_fail" does.

However lazy prerequisites aren't real tests, and are instead lazily
materialized in the guts of "test_have_prereq" when we've already
started another test.

We could detect the abort() (or similar) there and pass that exit code
down, and fail the test that caused the prerequisites to be
materialized.

But that would require extensive changes to test-lib.sh and
test-lib-functions.sh. Let's instead simply check if the exit code of
"test-tool regex" is zero, and if so set the prerequisites. If it's
non-zero let's run it again with "test_must_fail". We'll thus make a
distinction between "bad" non-zero (segv etc) and "good" (exit 1 etc.).

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

t/t7812-grep-icase-non-ascii.sh

@@ -11,9 +11,19 @@ test_expect_success GETTEXT_LOCALE 'setup' '
 	export LC_ALL
 '
 
-test_have_prereq GETTEXT_LOCALE &&
-test-tool regex "HALLÓ" "Halló" ICASE &&
-test_set_prereq REGEX_LOCALE
+test_expect_success GETTEXT_LOCALE 'setup REGEX_LOCALE prerequisite' '
+	# This "test-tool" invocation is identical...
+	if test-tool regex "HALLÓ" "Halló" ICASE
+	then
+		test_set_prereq REGEX_LOCALE
+	else
+
+		# ... to this one, but this way "test_must_fail" will
+		# tell a segfault or abort() from the regexec() test
+		# itself
+		test_must_fail test-tool regex "HALLÓ" "Halló" ICASE
+	fi
+'
 
 test_expect_success REGEX_LOCALE 'grep literal string, no -F' '
 	git grep -i "TILRAUN: Halló Heimur!" &&