Temporal: Add tests for addition/subtraction across era boundaries for Hijri calendars

test/intl402/Temporal/PlainDate/prototype/add/era-boundary-islamic-civil.js

@@ -0,0 +1,68 @@
+// 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.plaindate.prototype.add
+description: Adding years works correctly across era boundaries in islamic-civil calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDate.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date1.add(duration1),
+  0, 6, "M06", 15, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDate.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date2.add(duration1),
+  1, 6, "M06", 15, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDate.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date3.add(duration1),
+  2, 6, "M06", 15, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDate.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date4.add(new Temporal.Duration(10)),
+  6, 3, "M03", 1, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDate.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date5.add(duration1n),
+  1, 6, "M06", 15, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date3.add(duration1n),
+  0, 6, "M06", 15, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date2.add(duration1n),
+  -1, 6, "M06", 15, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDate.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date6.add(new Temporal.Duration(-10)),
+  -5, 3, "M03", 1, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDate/prototype/add/era-boundary-islamic-tbla.js

@@ -0,0 +1,68 @@
+// 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.plaindate.prototype.add
+description: Adding years works correctly across era boundaries in islamic-tbla calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDate.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date1.add(duration1),
+  0, 6, "M06", 15, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDate.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date2.add(duration1),
+  1, 6, "M06", 15, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDate.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date3.add(duration1),
+  2, 6, "M06", 15, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDate.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date4.add(new Temporal.Duration(10)),
+  6, 3, "M03", 1, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDate.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date5.add(duration1n),
+  1, 6, "M06", 15, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date3.add(duration1n),
+  0, 6, "M06", 15, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date2.add(duration1n),
+  -1, 6, "M06", 15, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDate.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date6.add(new Temporal.Duration(-10)),
+  -5, 3, "M03", 1, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDate/prototype/add/era-boundary-islamic-umalqura.js

@@ -0,0 +1,68 @@
+// 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.plaindate.prototype.add
+description: Adding years works correctly across era boundaries in islamic-umalqura calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDate.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date1.add(duration1),
+  0, 6, "M06", 15, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDate.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date2.add(duration1),
+  1, 6, "M06", 15, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDate.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date3.add(duration1),
+  2, 6, "M06", 15, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDate.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date4.add(new Temporal.Duration(10)),
+  6, 3, "M03", 1, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDate.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date5.add(duration1n),
+  1, 6, "M06", 15, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date3.add(duration1n),
+  0, 6, "M06", 15, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date2.add(duration1n),
+  -1, 6, "M06", 15, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDate.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date6.add(new Temporal.Duration(-10)),
+  -5, 3, "M03", 1, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDate/prototype/subtract/era-boundary-islamic-civil.js

@@ -0,0 +1,68 @@
+// 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.plaindate.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-civil calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDate.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date1.subtract(duration1),
+  0, 6, "M06", 15, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDate.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date2.subtract(duration1),
+  1, 6, "M06", 15, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDate.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date3.subtract(duration1),
+  2, 6, "M06", 15, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDate.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date4.subtract(new Temporal.Duration(-10)),
+  6, 3, "M03", 1, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDate.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date5.subtract(duration1n),
+  1, 6, "M06", 15, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date3.subtract(duration1n),
+  0, 6, "M06", 15, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date2.subtract(duration1n),
+  -1, 6, "M06", 15, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDate.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date6.subtract(new Temporal.Duration(10)),
+  -5, 3, "M03", 1, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDate/prototype/subtract/era-boundary-islamic-tbla.js

@@ -0,0 +1,68 @@
+// 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.plaindate.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-tbla calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDate.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date1.subtract(duration1),
+  0, 6, "M06", 15, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDate.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date2.subtract(duration1),
+  1, 6, "M06", 15, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDate.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date3.subtract(duration1),
+  2, 6, "M06", 15, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDate.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date4.subtract(new Temporal.Duration(-10)),
+  6, 3, "M03", 1, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDate.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date5.subtract(duration1n),
+  1, 6, "M06", 15, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date3.subtract(duration1n),
+  0, 6, "M06", 15, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date2.subtract(duration1n),
+  -1, 6, "M06", 15, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDate.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date6.subtract(new Temporal.Duration(10)),
+  -5, 3, "M03", 1, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDate/prototype/subtract/era-boundary-islamic-umalqura.js

@@ -0,0 +1,68 @@
+// 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.plaindate.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-umalqura calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDate.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date1.subtract(duration1),
+  0, 6, "M06", 15, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDate.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date2.subtract(duration1),
+  1, 6, "M06", 15, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDate.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date3.subtract(duration1),
+  2, 6, "M06", 15, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDate.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date4.subtract(new Temporal.Duration(-10)),
+  6, 3, "M03", 1, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDate.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date5.subtract(duration1n),
+  1, 6, "M06", 15, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date3.subtract(duration1n),
+  0, 6, "M06", 15, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDate(
+  date2.subtract(duration1n),
+  -1, 6, "M06", 15, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDate.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, calendar }, options);
+TemporalHelpers.assertPlainDate(
+  date6.subtract(new Temporal.Duration(10)),
+  -5, 3, "M03", 1, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDateTime/prototype/add/era-boundary-islamic-civil.js

@@ -0,0 +1,68 @@
+// 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.plaindatetime.prototype.add
+description: Adding years works correctly across era boundaries in islamic-civil calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.add(duration1),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.add(new Temporal.Duration(10)),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.add(duration1n),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1n),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1n),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.add(new Temporal.Duration(-10)),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDateTime/prototype/add/era-boundary-islamic-tbla.js

@@ -0,0 +1,68 @@
+// 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.plaindatetime.prototype.add
+description: Adding years works correctly across era boundaries in islamic-tbla calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.add(duration1),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.add(new Temporal.Duration(10)),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.add(duration1n),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1n),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1n),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.add(new Temporal.Duration(-10)),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDateTime/prototype/add/era-boundary-islamic-umalqura.js

@@ -0,0 +1,68 @@
+// 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.plaindatetime.prototype.add
+description: Adding years works correctly across era boundaries in islamic-umalqura calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.add(duration1),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.add(new Temporal.Duration(10)),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.add(duration1n),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1n),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1n),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.add(new Temporal.Duration(-10)),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDateTime/prototype/subtract/era-boundary-islamic-civil.js

@@ -0,0 +1,68 @@
+// 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.plaindatetime.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-civil calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.subtract(duration1),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.subtract(new Temporal.Duration(-10)),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.subtract(duration1n),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1n),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1n),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.subtract(new Temporal.Duration(10)),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDateTime/prototype/subtract/era-boundary-islamic-tbla.js

@@ -0,0 +1,68 @@
+// 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.plaindatetime.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-tbla calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.subtract(duration1),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.subtract(new Temporal.Duration(-10)),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.subtract(duration1n),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1n),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1n),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.subtract(new Temporal.Duration(10)),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/PlainDateTime/prototype/subtract/era-boundary-islamic-umalqura.js

@@ -0,0 +1,68 @@
+// 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.plaindatetime.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-umalqura calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.subtract(duration1),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.PlainDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.subtract(new Temporal.Duration(-10)),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.subtract(duration1n),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1n),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1n),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.PlainDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.subtract(new Temporal.Duration(10)),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/ZonedDateTime/prototype/add/era-boundary-islamic-civil.js

@@ -0,0 +1,68 @@
+// 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.zoneddatetime.prototype.add
+description: Adding years works correctly across era boundaries in islamic-civil calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.add(duration1).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1).toPlainDateTime(),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.add(new Temporal.Duration(10)).toPlainDateTime(),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.add(duration1n).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1n).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1n).toPlainDateTime(),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.add(new Temporal.Duration(-10)).toPlainDateTime(),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/ZonedDateTime/prototype/add/era-boundary-islamic-tbla.js

@@ -0,0 +1,68 @@
+// 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.zoneddatetime.prototype.add
+description: Adding years works correctly across era boundaries in islamic-tbla calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.add(duration1).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1).toPlainDateTime(),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.add(new Temporal.Duration(10)).toPlainDateTime(),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.add(duration1n).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1n).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1n).toPlainDateTime(),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.add(new Temporal.Duration(-10)).toPlainDateTime(),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/ZonedDateTime/prototype/add/era-boundary-islamic-umalqura.js

@@ -0,0 +1,68 @@
+// 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.zoneddatetime.prototype.add
+description: Adding years works correctly across era boundaries in islamic-umalqura calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(1);
+const duration1n = new Temporal.Duration(-1);
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.add(duration1).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1).toPlainDateTime(),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.add(new Temporal.Duration(10)).toPlainDateTime(),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.add(duration1n).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.add(duration1n).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.add(duration1n).toPlainDateTime(),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.add(new Temporal.Duration(-10)).toPlainDateTime(),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/ZonedDateTime/prototype/subtract/era-boundary-islamic-civil.js

@@ -0,0 +1,68 @@
+// 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.zoneddatetime.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-civil calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.subtract(duration1).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1).toPlainDateTime(),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.subtract(new Temporal.Duration(-10)).toPlainDateTime(),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.subtract(duration1n).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1n).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1n).toPlainDateTime(),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.subtract(new Temporal.Duration(10)).toPlainDateTime(),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/ZonedDateTime/prototype/subtract/era-boundary-islamic-tbla.js

@@ -0,0 +1,68 @@
+// 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.zoneddatetime.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-tbla calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.subtract(duration1).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1).toPlainDateTime(),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.subtract(new Temporal.Duration(-10)).toPlainDateTime(),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.subtract(duration1n).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1n).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1n).toPlainDateTime(),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.subtract(new Temporal.Duration(10)).toPlainDateTime(),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);

test/intl402/Temporal/ZonedDateTime/prototype/subtract/era-boundary-islamic-umalqura.js

@@ -0,0 +1,68 @@
+// 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.zoneddatetime.prototype.subtract
+description: Adding years works correctly across era boundaries in islamic-umalqura calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const duration1 = new Temporal.Duration(-1);
+const duration1n = new Temporal.Duration(1);
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+const date1 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date1.subtract(duration1).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 2 BH lands in 1 BH (counts backwards)",
+  "bh", 1
+);
+
+const date2 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 BH lands in 1 AH (no year zero)",
+  "ah", 1
+);
+
+const date3 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 1, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1).toPlainDateTime(),
+  2, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Adding 1 year to 1 AH lands in 2 AH",
+  "ah", 2
+);
+
+const date4 = Temporal.ZonedDateTime.from({ era: "bh", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date4.subtract(new Temporal.Duration(-10)).toPlainDateTime(),
+  6, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Adding 10 years to 5 BH lands in 6 AH (no year zero)",
+  "ah", 6
+);
+
+const date5 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 2, monthCode: "M06", day: 15, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date5.subtract(duration1n).toPlainDateTime(),
+  1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 2 AH lands in 1 AH",
+  "ah", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date3.subtract(duration1n).toPlainDateTime(),
+  0, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 AH lands in 1 BH",
+  "bh", 1
+);
+
+TemporalHelpers.assertPlainDateTime(
+  date2.subtract(duration1n).toPlainDateTime(),
+  -1, 6, "M06", 15, 12, 34, 0, 0, 0, 0, "Subtracting 1 year from 1 BH lands in 2 BH",
+  "bh", 2
+);
+
+const date6 = Temporal.ZonedDateTime.from({ era: "ah", eraYear: 5, monthCode: "M03", day: 1, hour: 12, minute: 34, timeZone: "UTC", calendar }, options);
+TemporalHelpers.assertPlainDateTime(
+  date6.subtract(new Temporal.Duration(10)).toPlainDateTime(),
+  -5, 3, "M03", 1, 12, 34, 0, 0, 0, 0, "Subtracting 10 years from 5 AH lands in 6 BH",
+  "bh", 6
+);