Intl Era Monthcode: DateTimeFormat.resolvedOptions().calendar

Tests the Intl.DateTimeFormat.prototype.resolvedOptions().calendar value
for each supported calendar.

Co-Authored-By: Philip Chimento <pchimento@igalia.com>

test/intl402/DateTimeFormat/prototype/resolvedOptions/calendar.js

@@ -0,0 +1,45 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-intl.datetimeformat.prototype.resolvedoptions
+description: Verifies that the calendar option is respected.
+locale: [en]
+features: [Intl.Era-monthcode]
+---*/
+
+const tests = [
+  "buddhist",
+  "chinese",
+  "coptic",
+  "dangi",
+  "ethioaa",
+  "ethiopic",
+  "gregory",
+  "hebrew",
+  "indian",
+  "islamic-civil",
+  "islamic-tbla",
+  "islamic-umalqura",
+  "iso8601",
+  "japanese",
+  "persian",
+  "roc",
+];
+
+for (const calendar of tests) {
+  const formatter = new Intl.DateTimeFormat("en", { calendar });
+  const options = formatter.resolvedOptions();
+  assert.sameValue(options.calendar, calendar, "Resolved calendar");
+}
+
+const aliases = [
+  ["ethiopic-amete-alem", "ethioaa"],
+  ["islamicc", "islamic-civil"],
+];
+
+for (const [alias, calendar] of aliases) {
+  const formatter = new Intl.DateTimeFormat("en", { calendar: alias });
+  const options = formatter.resolvedOptions();
+  assert.sameValue(options.calendar, calendar, "Resolved alias " + alias);
+}