tests: date: check that the hour format of the current locale is used

* tests/date/date-locale-hour.sh: New file.
* tests/local.mk (all_tests): Add the new test.

Co-authored-by: Pádraig Brady <P@draigBrady.com>

tests/date/date-locale-hour.sh

@@ -0,0 +1,40 @@
+#!/bin/sh
+# Check that 'date' uses the 12-hour or 24-hour clock depending on the
+# current locale.
+
+# Copyright (C) 2025 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ date
+
+locale date_fmt || skip_ "'locale date_fmt' not supported on this system"
+
+# Fallback C locale should be supported.
+for loc in "$LOCALE_FR_UTF8" 'en_US.UTF-8'; do
+  case $(LC_ALL="$loc" locale date_fmt) in
+    *%[Ilr]*)  compare_time='1:00' ;;
+    *%[HkRT]*) compare_time='13:00' ;;
+    *) skip_ 'unrecognised locale hour format';;
+  esac
+
+  case $(LC_ALL="$loc" date -d '2025-10-11T13:00') in
+    *"$compare_time"*) ;;
+    *) fail=1 ;;
+  esac
+done
+
+
+Exit $fail

tests/local.mk

@@ -317,6 +317,7 @@ all_tests =					\
   tests/date/date-debug.sh			\
   tests/date/date-ethiopia.sh			\
   tests/date/date-iran.sh			\
+  tests/date/date-locale-hour.sh		\
   tests/date/date-sec.sh			\
   tests/date/date-thailand.sh			\
   tests/date/date-tz.sh				\