tests: date: add tests for the Ethiopian calendar

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

tests/date/date-ethiopia.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+# Verify the Ethiopian calendar is used in the Ethiopian 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/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ date
+
+# Current year in the Gregorian calendar.
+current_year=$(LC_ALL=C date +%Y)
+
+export LC_ALL=am_ET.UTF-8
+
+if test "$(locale charmap 2>/dev/null)" != UTF-8; then
+  skip_ "Ethiopian UTF-8 locale not available"
+fi
+
+# 09-10 and 09-12 of the same Gregorian year are in different years in the
+# Ethiopian calendar.
+year_september_10=$(date -d $current_year-09-10 +%Y)
+year_september_12=$(date -d $current_year-09-12 +%Y)
+test $year_september_10 = $(($year_september_12 - 1)) || fail=1
+
+# The difference between the Gregorian year is 7 or 8 years.
+test $year_september_10 = $(($current_year - 8)) || fail=1
+test $year_september_12 = $(($current_year - 7)) || fail=1
+
+# Check that --iso-8601 and --rfc-3339 uses the Gregorian calendar.
+case $(date --iso-8601=hours) in $current_year-*) ;; *) fail=1 ;; esac
+case $(date --rfc-3339=date) in $current_year-*) ;; *) fail=1 ;; esac
+
+Exit $fail

tests/local.mk

@@ -309,6 +309,7 @@ all_tests =					\
   tests/csplit/csplit-io-err.sh			\
   tests/csplit/csplit-suppress-matched.pl	\
   tests/date/date-debug.sh			\
+  tests/date/date-ethiopia.sh			\
   tests/date/date-iran.sh			\
   tests/date/date-sec.sh			\
   tests/date/date-thailand.sh			\