Intl Era Monthcode: Add tests for PlainYearMonth addition in leap years

I had previously postponed adding these tests because they were affected
by tc39/proposal-temporal#3197. Now that TC39
has adopted a solution to that bug, we can add these and increase test
coverage for non-ISO8601 calendar addition in PlainYearMonth.

Author: ptomato

test/intl402/Temporal/PlainYearMonth/prototype/add/leap-months-chinese.js

@@ -0,0 +1,320 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.add
+description: Arithmetic around leap months in the chinese calendar
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "chinese";
+const options = { overflow: "reject" };
+
+// Years
+
+const years1 = new Temporal.Duration(1);
+const years1n = new Temporal.Duration(-1);
+
+const leap193807L = Temporal.PlainYearMonth.from({ year: 1938, monthCode: "M07L", calendar }, options);
+const leap195205L = Temporal.PlainYearMonth.from({ year: 1952, monthCode: "M05L", calendar }, options);
+const leap196603L = Temporal.PlainYearMonth.from({ year: 1966, monthCode: "M03L", calendar }, options);
+const common200008 = Temporal.PlainYearMonth.from({ year: 2000, monthCode: "M08", calendar }, options);
+const common200108 = Temporal.PlainYearMonth.from({ year: 2001, monthCode: "M08", calendar }, options);
+const common201901 = Temporal.PlainYearMonth.from({ year: 2019, monthCode: "M01", calendar }, options);
+const common201904 = Temporal.PlainYearMonth.from({ year: 2019, monthCode: "M04", calendar }, options);
+const leap202004 = Temporal.PlainYearMonth.from({ year: 2020, monthCode: "M04", calendar }, options);
+const leap202004L = Temporal.PlainYearMonth.from({ year: 2020, monthCode: "M04L", calendar }, options);
+const common202104 = Temporal.PlainYearMonth.from({ year: 2021, monthCode: "M04", calendar }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  common201901.add(years1),
+  2020, 1, "M01", "add 1 year from non-leap day",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap196603L.add(years1),
+  1967, 3, "M03", "Adding 1 year to leap month M03L lands in common-year M03 with overflow constrain",
+  undefined, undefined, null
+);
+
+assert.throws(RangeError, function () {
+  leap196603L.add(years1, options);
+}, "Adding 1 year to leap month rejects");
+
+TemporalHelpers.assertPlainYearMonth(
+  leap193807L.add(years1),
+  1939, 7, "M07", "Adding 1 year to leap month M07L on day 30 constrains to M07 day 29",
+  undefined, undefined, null
+);
+
+assert.throws(RangeError, function () {
+  leap193807L.add(years1, options);
+}, "Adding 1 year to leap month day 30 rejects");
+
+TemporalHelpers.assertPlainYearMonth(
+  common201904.add(years1, options),
+  2020, 4, "M04", "Adding 1 year to common-year M04 lands in leap-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004.add(years1, options),
+  2021, 4, "M04", "Adding 1 year to leap-year M04 lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 2012, monthCode: "M04L", calendar }, options).add(new Temporal.Duration(8), options),
+  2020, 5, "M04L", "Adding years to go from one M04L to the next M04L",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common200008.add(years1, options),
+  2001, 9, "M08", "Adding 1 year crossing leap month",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common201904.add(new Temporal.Duration(2), options),
+  2021, 4, "M04", "Adding 2 years to common-year M04 crossing leap year lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common201901.add(years1n),
+  2018, 1, "M01", "Subtracting 1 year from non-leap day",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap196603L.add(years1n),
+  1965, 3, "M03", "Subtracting 1 year from leap month M03L lands in common-year M03 with overflow constrain",
+  undefined, undefined, null
+);
+
+assert.throws(RangeError, function () {
+  leap196603L.add(years1n, options);
+}, "Subtracting 1 year from leap month rejects");
+
+TemporalHelpers.assertPlainYearMonth(
+  leap195205L.add(years1n),
+  1951, 5, "M05", "Subtracting 1 year from leap month M05L on day 30 constrains to M05 day 29",
+  undefined, undefined, null
+);
+
+assert.throws(RangeError, function () {
+  leap195205L.add(years1n, options);
+}, "Subtracting 1 year from leap month day 30 rejects");
+
+TemporalHelpers.assertPlainYearMonth(
+  common202104.add(years1n, options),
+  2020, 4, "M04", "Subtracting 1 year from common-year M04 lands in leap-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004.add(years1n, options),
+  2019, 4, "M04", "Subtracting 1 year from leap-year M04 lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004L.add(new Temporal.Duration(-8), options),
+  2012, 5, "M04L", "Subtracting years to go from one M04L to the previous M04L",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common200108.add(years1n, options),
+  2000, 8, "M08", "Subtracting 1 year crossing leap month",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common202104.add(new Temporal.Duration(-2), options),
+  2019, 4, "M04", "Subtracting 2 years from common-year M04 crossing leap year lands in common-year M04",
+  undefined, undefined, null
+);
+
+// Months
+
+const months1 = new Temporal.Duration(0, 1);
+const months1n = new Temporal.Duration(0, -1);
+const months12 = new Temporal.Duration(0, 12);
+const months12n = new Temporal.Duration(0, -12);
+const months13 = new Temporal.Duration(0, 13);
+const months13n = new Temporal.Duration(0, -13);
+
+const leap202003 = Temporal.PlainYearMonth.from({ year: 2020, monthCode: "M03", calendar }, options);
+const leap202006 = Temporal.PlainYearMonth.from({ year: 2020, monthCode: "M06", calendar }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 1947, monthCode: "M02L", calendar }, options).add(months1),
+  1947, 4, "M03", "add 1 month, starting at start of leap month",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 1955, monthCode: "M03L", calendar }, options).add(months1),
+  1955, 5, "M04", "add 1 month, starting at start of leap month with 30 days",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202003.add(months1),
+  2020, 4, "M04", "adding 1 month to M03 in leap year lands in M04 (not M04L)",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202003.add(new Temporal.Duration(0, 2)),
+  2020, 5, "M04L", "adding 2 months to M03 in leap year lands in M04L (leap month)",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202003.add(new Temporal.Duration(0, 3)),
+  2020, 6, "M05", "adding 3 months to M03 in leap year lands in M05 (not M06)",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common201904.add(months12),
+  2020, 4, "M04", "Adding 12 months to common-year M04 lands in leap-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common201904.add(months13),
+  2020, 5, "M04L", "Adding 13 months to common-year M04 lands in leap-year M04L",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004.add(months12),
+  2021, 3, "M03", "Adding 12 months to leap-year M04 lands in common-year M03",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004.add(months13),
+  2021, 4, "M04", "Adding 13 months to leap-year M04 lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004L.add(months12),
+  2021, 4, "M04", "Adding 12 months to M04L lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common200008.add(new Temporal.Duration(1, 12), options),
+  2002, 8, "M08", "Adding 1y 12mo crossing leap month in the year part",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common200108.add(new Temporal.Duration(2, 13), options),
+  2004, 9, "M08", "Adding 1y 13mo crossing leap month in the months part",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common201904.add(new Temporal.Duration(0, 24)),
+  2021, 3, "M03", "Adding 24 months to common-year M04 crossing leap year with M04L, lands in common-year M03",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common201904.add(new Temporal.Duration(0, 25)),
+  2021, 4, "M04", "Adding 25 months to common-year M04 crossing leap year with M04L, lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202006.add(months1n),
+  2020, 6, "M05", "Subtracting 1 month from M06 in leap year lands in M05",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202006.add(new Temporal.Duration(0, -2)),
+  2020, 5, "M04L", "Subtracting 2 months from M06 in leap year lands in M04L (leap month)",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202006.add(new Temporal.Duration(0, -3)),
+  2020, 4, "M04", "Subtracting 3 months from M06 in leap year lands in M04 (not M03)",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 2020, monthCode: "M05", calendar }, options).add(months1n),
+  2020, 5, "M04L", "Subtracting 1 month from M05 in leap year lands in M04L",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004L.add(months1n),
+  2020, 4, "M04", "Subtracting 1 month from M04L in calendar lands in M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common202104.add(months12n),
+  2020, 5, "M04L", "Subtracting 12 months from common-year M04 lands in leap-year M04L",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common202104.add(months13n),
+  2020, 4, "M04", "Subtracting 13 months from common-year M04 lands in leap-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004.add(months12n),
+  2019, 4, "M04", "Subtracting 12 months from leap-year M04 lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004L.add(months12n),
+  2019, 5, "M05", "Subtracting 12 months from M04L lands in common-year M05",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  leap202004L.add(months13n),
+  2019, 4, "M04", "Subtracting 13 months from M04L lands in common-year M04",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common200108.add(new Temporal.Duration(-1, -12), options),
+  1999, 8, "M08", "Adding 1y 12mo crossing leap month in the year part",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common200008.add(new Temporal.Duration(-2, -13), options),
+  1997, 8, "M08", "Adding 1y 13mo crossing leap month in the months part",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common202104.add(new Temporal.Duration(0, -24)),
+  2019, 5, "M05", "Subtracting 24 months from common-year M04 crossing leap year with M04L, lands in common-year M05",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  common202104.add(new Temporal.Duration(0, -25)),
+  2019, 4, "M04", "Subtracting 25 months from common-year M04 crossing leap year with M04L, lands in common-year M04",
+  undefined, undefined, null
+);