diff --git a/harness/temporalHelpers.js b/harness/temporalHelpers.js
index 45e12ef9d7c..42341d0644e 100644
--- a/harness/temporalHelpers.js
+++ b/harness/temporalHelpers.js
@@ -334,9 +334,15 @@ var TemporalHelpers = {
    * equal to an expected value. (Except the `calendar` property, since callers
    * may want to assert either object equality with an object they put in there,
    * or the value of yearMonth.calendarId.)
+   *
+   * Pass null as the referenceISODay if you don't want to give it explicitly.
+   * In that case, the expected referenceISODay will be computed using PlainDate
+   * and only verified for consistency, not for equality with a specific value.
    */
   assertPlainYearMonth(yearMonth, year, month, monthCode, description = "", era = undefined, eraYear = undefined, referenceISODay = 1) {
     const prefix = description ? `${description}: ` : "";
+    assert(typeof referenceISODay === "number" || referenceISODay === null,
+      `TemporalHelpers.assertPlainYearMonth() referenceISODay argument should be a number or null, not ${referenceISODay}`);
     assert(yearMonth instanceof Temporal.PlainYearMonth, `${prefix}instanceof`);
     assert.sameValue(
       TemporalHelpers.canonicalizeCalendarEra(yearMonth.calendarId, yearMonth.era),
@@ -348,7 +354,8 @@ var TemporalHelpers = {
     assert.sameValue(yearMonth.month, month, `${prefix}month result:`);
     assert.sameValue(yearMonth.monthCode, monthCode, `${prefix}monthCode result:`);
     const isoDay = Number(yearMonth.toString({ calendarName: "always" }).slice(1).split("-")[2].slice(0, 2));
-    assert.sameValue(isoDay, referenceISODay, `${prefix}referenceISODay result:`);
+    const expectedISODay = referenceISODay ?? yearMonth.toPlainDate({ day: 1 }).withCalendar("iso8601").day;
+    assert.sameValue(isoDay, expectedISODay, `${prefix}referenceISODay result:`);
   },
 
   /*
diff --git a/test/intl402/Temporal/PlainYearMonth/from/basic-hebrew.js b/test/intl402/Temporal/PlainYearMonth/from/basic-hebrew.js
new file mode 100644
index 00000000000..240c2863730
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/basic-hebrew.js
@@ -0,0 +1,26 @@
+// 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.from
+description: Basic functionality of resolving fields in hebrew calendar
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "hebrew";
+const options = { overflow: "reject" };
+
+const commonYear = 5783;
+
+for (let month = 1; month < 13; month++) {
+  const monthCode = `M${String(month).padStart(2, '0')}`;
+
+  const startOfMonth = Temporal.PlainYearMonth.from({ year: commonYear, month, calendar }, options);
+  TemporalHelpers.assertPlainYearMonth(
+    startOfMonth,
+    commonYear, month, monthCode,
+    `${monthCode} in common year`,
+    "am", commonYear, null
+  );
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/from/calendarresolvefields-error-ordering-gregory.js b/test/intl402/Temporal/PlainYearMonth/from/calendarresolvefields-error-ordering-gregory.js
new file mode 100644
index 00000000000..b12e83637fd
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/calendarresolvefields-error-ordering-gregory.js
@@ -0,0 +1,32 @@
+// 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.from
+description: CalendarResolveFields throws TypeError before RangeError (gregory calendar)
+info: |
+  CalendarResolveFields validates field types before validating field ranges,
+  ensuring TypeError is thrown before RangeError when both conditions exist.
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+// Missing year (and no era/eraYear) should throw TypeError even with month/monthCode conflict
+assert.throws(
+  TypeError,
+  () => Temporal.PlainYearMonth.from({ calendar: "gregory", monthCode: "M05", month: 6 }),
+  "Missing year/era throws TypeError before month/monthCode conflict throws RangeError"
+);
+
+// undefined year should throw TypeError even with month/monthCode conflict
+assert.throws(
+  TypeError,
+  () => Temporal.PlainYearMonth.from({ calendar: "gregory", year: undefined, monthCode: "M05", month: 6 }),
+  "undefined year throws TypeError before month/monthCode conflict throws RangeError"
+);
+
+// After type validation passes, range validation should throw RangeError
+assert.throws(
+  RangeError,
+  () => Temporal.PlainYearMonth.from({ calendar: "gregory", year: 2020, monthCode: "M05", month: 6 }),
+  "month/monthCode conflict throws RangeError when all types are valid"
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-ethiopic.js b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-ethiopic.js
new file mode 100644
index 00000000000..f4e8ea35ddb
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-ethiopic.js
@@ -0,0 +1,36 @@
+// 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.from
+description: Non-positive era years are remapped in ethiopic calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "ethiopic";
+const options = { overflow: "reject" };
+
+const am0 = Temporal.PlainYearMonth.from({ era: "am", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  am0,
+  0, 1, "M01", "AM 0 resolves to AA 5500",
+  "aa", 5500, null);
+
+const am1n = Temporal.PlainYearMonth.from({ era: "am", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  am1n,
+  -1, 1, "M01", "AM -1 resolves to AA 5499",
+  "aa", 5499, null);
+
+const aa0 = Temporal.PlainYearMonth.from({ era: "aa", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  aa0,
+  -5500, 1, "M01", "AA 0 is not remapped",
+  "aa", 0, null);
+
+const aa1n = Temporal.PlainYearMonth.from({ era: "aa", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  aa1n,
+  -5501, 1, "M01", "AA -1 is not remapped",
+  "aa", -1, null);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-gregory.js b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-gregory.js
new file mode 100644
index 00000000000..74ec706e88a
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-gregory.js
@@ -0,0 +1,36 @@
+// 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.from
+description: Non-positive era years are remapped in gregory calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "gregory";
+const options = { overflow: "reject" };
+
+const ce0 = Temporal.PlainYearMonth.from({ era: "ce", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ce0,
+  0, 1, "M01", "CE 0 resolves to BCE 1",
+  "bce", 1);
+
+const ce1n = Temporal.PlainYearMonth.from({ era: "ce", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ce1n,
+  -1, 1, "M01", "CE -1 resolves to BCE 2",
+  "bce", 2);
+
+const bce0 = Temporal.PlainYearMonth.from({ era: "bce", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bce0,
+  1, 1, "M01", "BCE 0 resolves to CE 1",
+  "ce", 1);
+
+const bce1n = Temporal.PlainYearMonth.from({ era: "bce", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bce1n,
+  2, 1, "M01", "BCE -1 resolves to CE 2",
+  "ce", 2);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-civil.js b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-civil.js
new file mode 100644
index 00000000000..da46fc77412
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-civil.js
@@ -0,0 +1,36 @@
+// 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.from
+description: Non-positive era years are remapped in islamic-civil calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+const ah0 = Temporal.PlainYearMonth.from({ era: "ah", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ah0,
+  0, 1, "M01", "AH 0 resolves to BH 1",
+  "bh", 1, null);
+
+const ah1n = Temporal.PlainYearMonth.from({ era: "ah", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ah1n,
+  -1, 1, "M01", "AH -1 resolves to BH 2",
+  "bh", 2, null);
+
+const bh0 = Temporal.PlainYearMonth.from({ era: "bh", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bh0,
+  1, 1, "M01", "BH 0 resolves to AH 1",
+  "ah", 1, null);
+
+const bh1n = Temporal.PlainYearMonth.from({ era: "bh", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bh1n,
+  2, 1, "M01", "BH -1 resolves to AH 2",
+  "ah", 2, null);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-tbla.js b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-tbla.js
new file mode 100644
index 00000000000..f8d65dffc39
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-tbla.js
@@ -0,0 +1,36 @@
+// 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.from
+description: Non-positive era years are remapped in islamic-tbla calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+const ah0 = Temporal.PlainYearMonth.from({ era: "ah", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ah0,
+  0, 1, "M01", "AH 0 resolves to BH 1",
+  "bh", 1, null);
+
+const ah1n = Temporal.PlainYearMonth.from({ era: "ah", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ah1n,
+  -1, 1, "M01", "AH -1 resolves to BH 2",
+  "bh", 2, null);
+
+const bh0 = Temporal.PlainYearMonth.from({ era: "bh", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bh0,
+  1, 1, "M01", "BH 0 resolves to AH 1",
+  "ah", 1, null);
+
+const bh1n = Temporal.PlainYearMonth.from({ era: "bh", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bh1n,
+  2, 1, "M01", "BH -1 resolves to AH 2",
+  "ah", 2, null);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-umalqura.js b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-umalqura.js
new file mode 100644
index 00000000000..7f9fddd8517
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-islamic-umalqura.js
@@ -0,0 +1,36 @@
+// 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.from
+description: Non-positive era years are remapped in islamic-umalqura calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+const ah0 = Temporal.PlainYearMonth.from({ era: "ah", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ah0,
+  0, 1, "M01", "AH 0 resolves to BH 1",
+  "bh", 1, null);
+
+const ah1n = Temporal.PlainYearMonth.from({ era: "ah", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ah1n,
+  -1, 1, "M01", "AH -1 resolves to BH 2",
+  "bh", 2, null);
+
+const bh0 = Temporal.PlainYearMonth.from({ era: "bh", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bh0,
+  1, 1, "M01", "BH 0 resolves to AH 1",
+  "ah", 1, null);
+
+const bh1n = Temporal.PlainYearMonth.from({ era: "bh", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bh1n,
+  2, 1, "M01", "BH -1 resolves to AH 2",
+  "ah", 2, null);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-japanese.js b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-japanese.js
index f804de957bd..20f8436fd73 100644
--- a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-japanese.js
+++ b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-japanese.js
@@ -4,26 +4,188 @@
 /*---
 esid: sec-temporal.plainyearmonth.from
 description: >
-  Dates in same year before era starts should resolve to previous era
+  Dates in same year or years before era starts should resolve to previous era
   (Japanese calendar)
 includes: [temporalHelpers.js]
 features: [Temporal, Intl.Era-monthcode]
 ---*/
 
 const calendar = "japanese";
+const options = { overflow: "reject" };
 
-const reiwa = Temporal.PlainYearMonth.from({ era: "reiwa", eraYear: 1, month: 1,  calendar });
-const heisei = Temporal.PlainYearMonth.from({ era: "heisei", eraYear: 1, month: 1,  calendar });
-const showa = Temporal.PlainYearMonth.from({ era: "showa", eraYear: 1, month: 1,  calendar });
-const taisho = Temporal.PlainYearMonth.from({ era: "taisho", eraYear: 1, month: 1,  calendar });
-const meiji = Temporal.PlainYearMonth.from({ era: "meiji", eraYear: 1, month: 1,  calendar });
+const reiwa1BeforeStart = Temporal.PlainYearMonth.from({ era: "reiwa", eraYear: 1, monthCode: "M04", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  reiwa1BeforeStart,
+  2019, 4, "M04", "Reiwa 1 resolves to Heisei 31 before era start date",
+  "heisei", 31);
 
-TemporalHelpers.assertPlainYearMonth(reiwa, 2019, 1, "M01",  "Reiwa resolves to Heisei", "heisei", 31);
+const reiwa0 = Temporal.PlainYearMonth.from({ era: "reiwa", eraYear: 0, monthCode: "M05", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  reiwa0,
+  2018, 5, "M05", "Reiwa 0 resolves to Heisei 30",
+  "heisei", 30);
 
-TemporalHelpers.assertPlainYearMonth(heisei, 1989, 1, "M01",  "Heisei resolves to Showa", "showa", 64);
+const reiwa1n = Temporal.PlainYearMonth.from({ era: "reiwa", eraYear: -1, monthCode: "M05", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  reiwa1n,
+  2017, 5, "M05", "Reiwa -1 resolves to Heisei 29",
+  "heisei", 29);
 
-TemporalHelpers.assertPlainYearMonth(showa, 1926, 1, "M01",  "Showa resolves to Taisho", "taisho", 15);
+const heisei31AfterStart = Temporal.PlainYearMonth.from({ era: "heisei", eraYear: 31, monthCode: "M05", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  heisei31AfterStart,
+  2019, 5, "M05", "Heisei 31 resolves to Reiwa 1 after era start date",
+  "reiwa", 1);
 
-TemporalHelpers.assertPlainYearMonth(taisho, 1912, 1, "M01",  "Taisho resolves to Meiji", "meiji", 45);
+const heisei1BeforeStart = Temporal.PlainYearMonth.from({ era: "heisei", eraYear: 1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  heisei1BeforeStart,
+  1989, 1, "M01", "Heisei 1 resolves to Showa 64 before era start date",
+  "showa", 64);
 
-TemporalHelpers.assertPlainYearMonth(meiji, 1868, 1, "M01",  "Meiji resolves to CE", "ce", 1868);
+const heisei0 = Temporal.PlainYearMonth.from({ era: "heisei", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  heisei0,
+  1988, 1, "M01", "Heisei 0 resolves to Showa 63",
+  "showa", 63);
+
+const heisei1n = Temporal.PlainYearMonth.from({ era: "heisei", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  heisei1n,
+  1987, 1, "M01", "Heisei -1 resolves to Showa 62",
+  "showa", 62);
+
+const showa64AfterStart = Temporal.PlainYearMonth.from({ era: "showa", eraYear: 64, monthCode: "M02", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  showa64AfterStart,
+  1989, 2, "M02", "Showa 64 resolves to Heisei 1 after era start date",
+  "heisei", 1);
+
+const showa1BeforeStart = Temporal.PlainYearMonth.from({ era: "showa", eraYear: 1, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  showa1BeforeStart,
+  1926, 12, "M12", "Showa 1 resolves to Taisho 15 before era start date",
+  "taisho", 15);
+
+const showa0 = Temporal.PlainYearMonth.from({ era: "showa", eraYear: 0, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  showa0,
+  1925, 12, "M12", "Showa 0 resolves to Taisho 14",
+  "taisho", 14);
+
+const showa1n = Temporal.PlainYearMonth.from({ era: "showa", eraYear: -1, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  showa1n,
+  1924, 12, "M12", "Showa -1 resolves to Taisho 13",
+  "taisho", 13);
+
+// There is no PlainYearMonth in which Taisho 15 resolves to Showa 1
+const taisho16 = Temporal.PlainYearMonth.from({ era: "taisho", eraYear: 16, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  taisho16,
+  1927, 1, "M01", "Taisho 16 resolves to Showa 2",
+  "showa", 2);
+
+const taisho1BeforeStart = Temporal.PlainYearMonth.from({ era: "taisho", eraYear: 1, monthCode: "M07", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  taisho1BeforeStart,
+  1912, 7, "M07", "Taisho 1 resolves to Meiji 45 before era start date",
+  "meiji", 45);
+
+const taisho0 = Temporal.PlainYearMonth.from({ era: "taisho", eraYear: 0, monthCode: "M07", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  taisho0,
+  1911, 7, "M07", "Taisho 0 resolves to Meiji 44",
+  "meiji", 44);
+
+const taisho1n = Temporal.PlainYearMonth.from({ era: "taisho", eraYear: -1, monthCode: "M07", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  taisho1n,
+  1910, 7, "M07", "Taisho -1 resolves to Meiji 43",
+  "meiji", 43);
+
+const meiji45AfterStart = Temporal.PlainYearMonth.from({ era: "meiji", eraYear: 45, monthCode: "M08", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  meiji45AfterStart,
+  1912, 8, "M08", "Meiji 45 resolves to Taisho 1 after era start date",
+  "taisho", 1);
+
+const meiji1BeforeStart = Temporal.PlainYearMonth.from({ era: "meiji", eraYear: 1, monthCode: "M10", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  meiji1BeforeStart,
+  1868, 10, "M10", "Meiji 1 resolves to CE 1868 before era start date",
+  "ce", 1868);
+
+const meiji0 = Temporal.PlainYearMonth.from({ era: "meiji", eraYear: 0, monthCode: "M10", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  meiji0,
+  1867, 10, "M10", "Meiji 0 resolves to CE 1867",
+  "ce", 1867);
+
+const meiji1n = Temporal.PlainYearMonth.from({ era: "meiji", eraYear: -1, monthCode: "M10", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  meiji1n,
+  1866, 10, "M10", "Meiji -1 resolves to CE 1866",
+  "ce", 1866);
+
+const ce1868AfterStart = Temporal.PlainYearMonth.from({ era: "ce", eraYear: 1868, monthCode: "M11", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ce1868AfterStart,
+  1868, 11, "M11", "CE 1868 resolves to Meiji 1 after era start date",
+  "meiji", 1);
+
+const ce0 = Temporal.PlainYearMonth.from({ era: "ce", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ce0,
+  0, 1, "M01", "CE 0 resolves to BCE 1",
+  "bce", 1);
+
+const ce1n = Temporal.PlainYearMonth.from({ era: "ce", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ce1n,
+  -1, 1, "M01", "CE -1 resolves to BCE 2",
+  "bce", 2);
+
+const bce0 = Temporal.PlainYearMonth.from({ era: "bce", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bce0,
+  1, 1, "M01", "BCE 0 resolves to CE 1",
+  "ce", 1);
+
+const bce1n = Temporal.PlainYearMonth.from({ era: "bce", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  bce1n,
+  2, 1, "M01", "BCE -1 resolves to CE 2",
+  "ce", 2);
+
+// Years far after the end of an era
+
+const heisei100 = Temporal.PlainYearMonth.from({ era: "heisei", eraYear: 100, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  heisei100,
+  2088, 12, "M12", "Heisei 100 resolves to Reiwa 70",
+  "reiwa", 70);
+
+const showa100 = Temporal.PlainYearMonth.from({ era: "showa", eraYear: 100, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  showa100,
+  2025, 12, "M12", "Showa 100 resolves to Reiwa 7",
+  "reiwa", 7);
+
+const taisho100 = Temporal.PlainYearMonth.from({ era: "taisho", eraYear: 100, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  taisho100,
+  2011, 12, "M12", "Taisho 100 resolves to Heisei 23",
+  "heisei", 23);
+
+const meiji100 = Temporal.PlainYearMonth.from({ era: "meiji", eraYear: 100, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  meiji100,
+  1967, 12, "M12", "Meiji 100 resolves to Showa 42",
+  "showa", 42);
+
+const ce2000 = Temporal.PlainYearMonth.from({ era: "ce", eraYear: 2000, monthCode: "M12", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  ce2000,
+  2000, 12, "M12", "CE 2000 resolves to Heisei 12",
+  "heisei", 12);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/era-boundary-roc.js b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-roc.js
new file mode 100644
index 00000000000..d89e78892d1
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/era-boundary-roc.js
@@ -0,0 +1,36 @@
+// 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.from
+description: Non-positive era years are remapped in roc calendar
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "roc";
+const options = { overflow: "reject" };
+
+const roc0 = Temporal.PlainYearMonth.from({ era: "roc", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  roc0,
+  0, 1, "M01", "ROC 0 resolves to BROC 1",
+  "broc", 1);
+
+const roc1n = Temporal.PlainYearMonth.from({ era: "roc", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  roc1n,
+  -1, 1, "M01", "ROC -1 resolves to BROC 2",
+  "broc", 2);
+
+const broc0 = Temporal.PlainYearMonth.from({ era: "broc", eraYear: 0, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  broc0,
+  1, 1, "M01", "BROC 0 resolves to ROC 1",
+  "roc", 1);
+
+const broc1n = Temporal.PlainYearMonth.from({ era: "broc", eraYear: -1, monthCode: "M01", calendar }, options);
+TemporalHelpers.assertPlainYearMonth(
+  broc1n,
+  2, 1, "M01", "BROC -1 resolves to ROC 2",
+  "roc", 2);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/invalid-month-codes-hebrew.js b/test/intl402/Temporal/PlainYearMonth/from/invalid-month-codes-hebrew.js
new file mode 100644
index 00000000000..5e5cbac8ee4
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/invalid-month-codes-hebrew.js
@@ -0,0 +1,24 @@
+// 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.from
+description: Month codes that are invalid for Hebrew calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "hebrew";
+
+assert.throws(RangeError, () => {
+  Temporal.PlainYearMonth.from({ year: 5779, monthCode: "M13", calendar });
+}, "M13 should not be a valid month code");
+
+// Invalid leap months: e.g. M02L
+for (var i = 1; i <= 12; i++) {
+  if (i === 5)
+    continue;
+  const monthCode = `M${ i.toString().padStart(2, "0") }L`;
+  assert.throws(RangeError, function () {
+    Temporal.PlainYearMonth.from({ year: 5779, monthCode, calendar });
+  });
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/from/leap-months-hebrew.js b/test/intl402/Temporal/PlainYearMonth/from/leap-months-hebrew.js
new file mode 100644
index 00000000000..32b03ff5841
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/leap-months-hebrew.js
@@ -0,0 +1,35 @@
+// 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.from
+description: Test valid leap months when resolving fields in hebrew calendar
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "hebrew";
+
+// Valid leap month: Adar I 5779
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 5779, month: 6, calendar }),
+  5779, 6, "M05L",
+  "Leap month resolved from month number",
+  "am", 5779, null);
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 5779, monthCode: "M05L", calendar }),
+  5779, 6, "M05L",
+  "Leap month resolved from month code",
+  "am", 5779, null);
+
+// Creating dates in later months in a leap year
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 5779, month: 7, calendar }),
+  5779, 7, "M06",
+  "Month after leap month resolved from month number",
+  "am", 5779, null);
+TemporalHelpers.assertPlainYearMonth(
+  Temporal.PlainYearMonth.from({ year: 5779, monthCode: "M06", calendar }),
+  5779, 7, "M06",
+  "Month after leap month resolved from month code",
+  "am", 5779, null);
diff --git a/test/intl402/Temporal/PlainYearMonth/from/leap-year-hebrew.js b/test/intl402/Temporal/PlainYearMonth/from/leap-year-hebrew.js
new file mode 100644
index 00000000000..8be03cac5d0
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/leap-year-hebrew.js
@@ -0,0 +1,43 @@
+// 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.from
+description: Basic functionality of resolving fields in hebrew calendar leap year
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "hebrew";
+const options = { overflow: "reject" };
+
+const leapYear = 5784;
+const monthCodes5784 = [
+  undefined,
+  "M01",
+  "M02",
+  "M03",
+  "M04",
+  "M05",
+  "M05L",
+  "M06",
+  "M07",
+  "M08",
+  "M09",
+  "M10",
+  "M11",
+  "M12"
+];
+
+for (let month = 1; month < 14; month++) {
+  const monthCode = monthCodes5784[month];
+
+  const instance = Temporal.PlainYearMonth.from({ year: leapYear, month, calendar }, options);
+  TemporalHelpers.assertPlainYearMonth(
+    instance,
+    leapYear, month, monthCode,
+    `month ${monthCode} in leap year`,
+    "am", leapYear, null
+  );
+}
+
diff --git a/test/intl402/Temporal/PlainYearMonth/from/non-positive-single-era-year.js b/test/intl402/Temporal/PlainYearMonth/from/non-positive-single-era-year.js
new file mode 100644
index 00000000000..b1bef4cc4cd
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/non-positive-single-era-year.js
@@ -0,0 +1,29 @@
+// 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.from
+description: Non-positive era years in calendars with a single era
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendarEras = {
+  buddhist: "be",
+  coptic: "am",
+  ethioaa: "aa",
+  hebrew: "am",
+  indian: "shaka",
+  persian: "ap",
+};
+const options = { overflow: "reject" };
+
+for (const [calendar, era] of Object.entries(calendarEras)) {
+  for (const eraYear of [-1, 0, 1]) {
+    const date = Temporal.PlainYearMonth.from({ era, eraYear, monthCode: "M01", calendar }, options);
+    TemporalHelpers.assertPlainYearMonth(
+      date,
+      eraYear, 1, "M01", `era year ${eraYear} is not remapped`,
+      era, eraYear, null);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/from/roundtrip-from-property-bag.js b/test/intl402/Temporal/PlainYearMonth/from/roundtrip-from-property-bag.js
new file mode 100644
index 00000000000..a880a1f6999
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/from/roundtrip-from-property-bag.js
@@ -0,0 +1,96 @@
+// 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.from
+description: >
+  Check that various dates created from a property bag have the expected
+  properties
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+
+const cases = [
+  ["buddhist", 2543, 1, "M01", "be", 2543, "month containing ISO date 2000-01-01"],
+  ["chinese", 1999, 11, "M11", undefined, undefined, "month containing ISO date 2000-01-01"],
+  ["coptic", 1716, 4, "M04", "am", 1716, "month containing ISO date 2000-01-01"],
+  ["dangi", 1999, 11, "M11", undefined, undefined, "month containing ISO date 2000-01-01"],
+  ["ethioaa", 7492, 4, "M04", "aa", 7492, "month containing ISO date 2000-01-01"],
+  ["ethiopic", 1992, 4, "M04", "am", 1992, "month containing ISO date 2000-01-01"],
+  ["gregory", 2000, 1, "M01", "ce", 2000, "month containing ISO date 2000-01-01"],
+  ["hebrew", 5760, 4, "M04", "am", 5760, "month containing ISO date 2000-01-01"],
+  ["indian", 1921, 10, "M10", "shaka", 1921, "month containing ISO date 2000-01-01"],
+  ["islamic-civil", 1420, 9, "M09", "ah", 1420, "month containing ISO date 2000-01-01"],
+  ["islamic-tbla", 1420, 9, "M09", "ah", 1420, "month containing ISO date 2000-01-01"],
+  ["islamic-umalqura", 1420, 9, "M09", "ah", 1420, "month containing ISO date 2000-01-01"],
+  ["japanese", 2000, 1, "M01", "heisei", 12, "month containing ISO date 2000-01-01"],
+  ["persian", 1378, 10, "M10", "ap", 1378, "month containing ISO date 2000-01-01"],
+  ["roc", 89, 1, "M01", "roc", 89, "month containing ISO date 2000-01-01"],
+
+  ["buddhist", 544, 1, "M01", "be", 544, "month containing ISO date 0001-01-01"],
+  // ["chinese", 0, 12, "M11", undefined, undefined, "month containing ISO date 0001-01-01"], // (out of specified range)
+  ["coptic", -283, 5, "M05", "am", -283, "month containing ISO date 0001-01-01"],
+  // ["dangi", 0, 12, "M11", undefined, undefined, "month containing ISO date 0001-01-01"], // (out of specified range)
+  ["ethioaa", 5493, 5, "M05", "aa", 5493, "month containing ISO date 0001-01-01"],
+  ["ethiopic", -7, 5, "M05", "aa", 5493, "month containing ISO date 0001-01-01"],
+  ["gregory", 1, 1, "M01", "ce", 1, "month containing ISO date 0001-01-01"],
+  ["hebrew", 3761, 4, "M04", "am", 3761, "month containing ISO date 0001-01-01"],
+  ["indian", -78, 10, "M10", "shaka", -78, "month containing ISO date 0001-01-01"],
+  ["islamic-civil", -640, 5, "M05", "bh", 641, "month containing ISO date 0001-01-01"],
+  ["islamic-tbla", -640, 5, "M05", "bh", 641, "month containing ISO date 0001-01-01"],
+  ["islamic-umalqura", -640, 5, "M05", "bh", 641, "month containing ISO date 0001-01-01"],
+  ["japanese", 1, 1, "M01", "ce", 1, "month containing ISO date 0001-01-01"],
+  ["persian", -621, 10, "M10", "ap", -621, "month containing ISO date 0001-01-01"],
+  ["roc", -1910, 1, "M01", "broc", 1911, "month containing ISO date 0001-01-01"],
+
+  // Additional cases that were moved in from staging tests, or that we add to
+  // catch regressions
+  ["chinese", 1900, 1, "M01", undefined, undefined, "start of non-approximated range"],
+  ["chinese", 2099, 13, "M12", undefined, undefined, "end of non-approximated range"],
+  ["dangi", 1900, 1, "M01", undefined, undefined, "start of non-approximated range"],
+  ["dangi", 2049, 12, "M12", undefined, undefined, "end of non-approximated range"],
+  ["islamic-civil", 1445, 1, "M01", "ah", 1445, "recent year"],
+  ["islamic-tbla", 1445, 1, "M01", "ah", 1445, "recent year"],
+  ["islamic-umalqura", 1445, 1, "M01", "ah", 1445, "recent year"],
+  ["islamic-umalqura", -6823, 1, "M01", "bh", 6824, "https://github.com/unicode-org/icu4x/issues/4914"],
+  ["persian", 1395, 1, "M01", "ap", 1395, "leap year 1395"],
+  ["persian", 1396, 1, "M01", "ap", 1396, "common year 1396"],
+  ["persian", 1397, 1, "M01", "ap", 1397, "common year 1397"],
+  ["persian", 1398, 1, "M01", "ap", 1398, "common year 1398"],
+  ["persian", 1399, 1, "M01", "ap", 1399, "leap year 1399"],
+  ["persian", 1400, 1, "M01", "ap", 1400, "common year 1400"],
+];
+
+for (const [calendar, year, month, monthCode, era, eraYear, descr] of cases) {
+  const dateFromYearMonth = Temporal.PlainYearMonth.from({ year, month, calendar }, options);
+  TemporalHelpers.assertPlainYearMonth(
+    dateFromYearMonth,
+    year, month, monthCode,
+    `${descr} (${calendar}) - created from year and month`,
+    era, eraYear, null);
+
+  const dateFromYearMonthCode = Temporal.PlainYearMonth.from({ year, monthCode, calendar }, options);
+  TemporalHelpers.assertPlainYearMonth(
+    dateFromYearMonthCode,
+    year, month, monthCode,
+    `${descr} (${calendar}) - created from year and month code`,
+    era, eraYear, null);
+
+  if (era === undefined) continue;  // skip era-less calendars
+
+  const dateFromEraMonth = Temporal.PlainYearMonth.from({ era, eraYear, month, calendar }, options);
+  TemporalHelpers.assertPlainYearMonth(
+    dateFromEraMonth,
+    year, month, monthCode,
+    `${descr} (${calendar}) - created from era, era year, and month`,
+    era, eraYear, null);
+
+  const dateFromEraMonthCode = Temporal.PlainYearMonth.from({ era, eraYear, monthCode, calendar }, options);
+  TemporalHelpers.assertPlainYearMonth(
+    dateFromEraMonthCode,
+    year, month, monthCode,
+    `${descr} (${calendar}) - created from era, era year, and month code`,
+    era, eraYear, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-buddhist.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-buddhist.js
new file mode 100644
index 00000000000..70c306e4867
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-buddhist.js
@@ -0,0 +1,56 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the Buddhist calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "buddhist";
+const options = { overflow: "reject" };
+
+// 2515 = ISO year 1972
+// 2515 is a leap year; 2516 is a common year
+
+const sampleYears = {
+  2515: [
+    31,
+    29,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+  ],
+  2516: [
+    31,
+    28,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < 13; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-chinese.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-chinese.js
new file mode 100644
index 00000000000..a6384837098
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-chinese.js
@@ -0,0 +1,55 @@
+// 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.daysinmonth
+description: Days in each month in the Chinese calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "chinese";
+const options = { overflow: "reject" };
+
+// 1971 is a leap year; 1972 is a common year
+
+const sampleYears = {
+  1971: [
+    29,
+    30,
+    29,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+    30,
+    30,
+    29,
+  ],
+  1972: [
+    29,
+    30,
+    29,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+    30,
+    29,
+    30,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < daysInMonth.length; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-coptic.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-coptic.js
new file mode 100644
index 00000000000..9f764887074
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-coptic.js
@@ -0,0 +1,33 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the Coptic calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "coptic";
+const options = { overflow: "reject" };
+
+// 1687 = ISO year 1971
+// 1687 is a leap year; 1688 is a common year
+
+const leapYear = 1687;
+const commonYear = 1688;
+
+for (var year of [leapYear, commonYear]) {
+  for (var month = 1; month < 14; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    if (month !== 13)
+      assert.sameValue(date.daysInMonth, 30, `${date}`);
+    else if (year == leapYear)
+      assert.sameValue(date.daysInMonth, 6, `${date}`);
+    else
+      assert.sameValue(date.daysInMonth, 5, `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-dangi.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-dangi.js
new file mode 100644
index 00000000000..7e95ecff32e
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-dangi.js
@@ -0,0 +1,55 @@
+// 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.daysinmonth
+description: Days in each month in the Dangi calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "dangi";
+const options = { overflow: "reject" };
+
+// 1971 is a common year; 1972 is a leap year
+
+const sampleYears = {
+  1971: [
+    29,
+    30,
+    29,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+    30,
+    30,
+    29,
+  ],
+  1972: [
+    29,
+    30,
+    29,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+    30,
+    30,
+    29,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < daysInMonth.length; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-ethioaa.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-ethioaa.js
new file mode 100644
index 00000000000..db85ed47496
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-ethioaa.js
@@ -0,0 +1,33 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the ethioaa calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "ethioaa";
+const options = { overflow: "reject" };
+
+// 7463 = ISO year 1971
+// 7463 is a leap year; 7464 is a common year
+
+const leapYear = 7463;
+const commonYear = 7464;
+
+for (var year of [leapYear, commonYear]) {
+  for (var month = 1; month < 14; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    if (month !== 13)
+      assert.sameValue(date.daysInMonth, 30, `${date}`);
+    else if (year == leapYear)
+      assert.sameValue(date.daysInMonth, 6, `${date}`);
+    else
+      assert.sameValue(date.daysInMonth, 5, `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-ethiopic.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-ethiopic.js
new file mode 100644
index 00000000000..7a8f3090a24
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-ethiopic.js
@@ -0,0 +1,33 @@
+// 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.daysinmonth
+description: Days in each month in the ethiopic calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "ethiopic";
+const options = { overflow: "reject" };
+
+// 1963 = ISO year 1971
+// 1963 is a leap year; 1964 is a common year
+
+const leapYear = 1963;
+const commonYear = 1964;
+
+for (var year of [leapYear, commonYear]) {
+  for (var month = 1; month < 14; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    if (month !== 13)
+      assert.sameValue(date.daysInMonth, 30, `${date}`);
+    else if (year == leapYear)
+      assert.sameValue(date.daysInMonth, 6, `${date}`);
+    else
+      assert.sameValue(date.daysInMonth, 5, `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-gregory.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-gregory.js
new file mode 100644
index 00000000000..0fa9702b21b
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-gregory.js
@@ -0,0 +1,57 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the gregory calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "gregory";
+const options = { overflow: "reject" };
+
+// 1972 is a leap year; 1973 is a common year
+
+const sampleYears = {
+  1972: [
+    31,
+    29,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+  ],
+  1973: [
+    31,
+    28,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < 13; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-hebrew.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-hebrew.js
new file mode 100644
index 00000000000..9026d0b49a7
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-hebrew.js
@@ -0,0 +1,58 @@
+// 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.daysinmonth
+description: Days in each month in the Hebrew calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "hebrew";
+const options = { overflow: "reject" };
+
+// 5732 = ISO year 1972
+// 5732 is a common year; 5730 is a leap year
+
+const sampleYears = {
+  5730: [
+    30,
+    29,
+    29,
+    29,
+    30,
+    30,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+    29,
+  ],
+  5732: [
+    30,
+    30,
+    30,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+    29,
+    29,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < daysInMonth.length; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-indian.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-indian.js
new file mode 100644
index 00000000000..a3a2f876f02
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-indian.js
@@ -0,0 +1,58 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the Indian calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "indian";
+const options = { overflow: "reject" };
+
+// 1894 = ISO year 1972
+// 1894 is a leap year; 1895 is a common year
+
+const sampleYears = {
+  1894: [
+    31,
+    31,
+    31,
+    31,
+    31,
+    31,
+    30,
+    30,
+    30,
+    30,
+    30,
+    30,
+    30,
+  ],
+  1895: [
+    30,
+    31,
+    31,
+    31,
+    31,
+    31,
+    30,
+    30,
+    30,
+    30,
+    30,
+    30,
+    30,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < daysInMonth.length; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-civil.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-civil.js
new file mode 100644
index 00000000000..6922618cd8c
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-civil.js
@@ -0,0 +1,60 @@
+// 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.daysinmonth
+description: Days in each month in the islamic-civil calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "islamic-civil";
+const options = { overflow: "reject" };
+
+// 1390 = ISO year 1970
+const leapYear = 1390;
+const commonYear = 1391;
+
+const leapYearDaysInMonth = [
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  30
+];
+
+const commonYearDaysInMonth = [
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29
+];
+
+const daysInMonth = {};
+daysInMonth[leapYear] = leapYearDaysInMonth;
+daysInMonth[commonYear] = commonYearDaysInMonth;
+
+for (let year of [leapYear, commonYear]) {
+  for (var month = 1; month < 13; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[year][month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-tbla.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-tbla.js
new file mode 100644
index 00000000000..a9b5d679727
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-tbla.js
@@ -0,0 +1,60 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the islamic-tbla calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "islamic-tbla";
+const options = { overflow: "reject" };
+
+// 1390 = ISO year 1970
+const leapYear = 1390;
+const commonYear = 1391;
+
+const leapYearDaysInMonth = [
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  30
+];
+
+const commonYearDaysInMonth = [
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29,
+  30,
+  29
+];
+
+const daysInMonth = {};
+daysInMonth[leapYear] = leapYearDaysInMonth;
+daysInMonth[commonYear] = commonYearDaysInMonth;
+
+for (let year of [leapYear, commonYear]) {
+  for (var month = 1; month < 13; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[year][month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-umalqura.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-umalqura.js
new file mode 100644
index 00000000000..db1d009479b
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-islamic-umalqura.js
@@ -0,0 +1,54 @@
+// 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.daysinmonth
+description: Days in each month in the islamic-umalqura calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "islamic-umalqura";
+const options = { overflow: "reject" };
+
+// 1390 = ISO year 1970
+const sampleYears = {
+  1390: [
+    29,
+    30,
+    29,
+    30,
+    30,
+    30,
+    29,
+    30,
+    29,
+    30,
+    29,
+    30,
+  ],
+  1391: [
+    29,
+    29,
+    30,
+    29,
+    30,
+    30,
+    29,
+    30,
+    30,
+    29,
+    30,
+    29
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < 13; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-japanese.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-japanese.js
new file mode 100644
index 00000000000..cdae1c9a145
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-japanese.js
@@ -0,0 +1,55 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the Japanese calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "japanese";
+const options = { overflow: "reject" };
+
+// 1972 is a leap year; 1973 is a common year
+
+const sampleYears = {
+  1972: [
+    31,
+    29,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+  ],
+  1973: [
+    31,
+    28,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < daysInMonth.length; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-persian.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-persian.js
new file mode 100644
index 00000000000..a8a057d146f
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-persian.js
@@ -0,0 +1,55 @@
+// 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.daysinmonth
+description: Days in each month in the Persian calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "persian";
+const options = { overflow: "reject" };
+
+// 1350 is a leap year; 1351 is a common year
+
+const sampleYears = {
+  1350: [
+    31,
+    31,
+    31,
+    31,
+    31,
+    31,
+    30,
+    30,
+    30,
+    30,
+    30,
+    30,
+  ],
+  1351: [
+    31,
+    31,
+    31,
+    31,
+    31,
+    31,
+    30,
+    30,
+    30,
+    30,
+    30,
+    29,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < daysInMonth.length; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-roc.js b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-roc.js
new file mode 100644
index 00000000000..cefd54d0273
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/daysInMonth/basic-roc.js
@@ -0,0 +1,55 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.daysinmonth
+description: Days in each month in the roc calendar
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const calendar = "roc";
+const options = { overflow: "reject" };
+
+// 61 is a leap year; 62 is a common year
+
+const sampleYears = {
+  61: [
+    31,
+    29,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+  ],
+  62: [
+    31,
+    28,
+    31,
+    30,
+    31,
+    30,
+    31,
+    31,
+    30,
+    31,
+    30,
+    31,
+  ]
+};
+
+for (var [year, daysInMonth] of Object.entries(sampleYears)) {
+  for (var month = 1; month < daysInMonth.length; month++) {
+    const date = Temporal.PlainYearMonth.from({
+      year,
+      month,
+      calendar
+    });
+    assert.sameValue(date.daysInMonth, daysInMonth[month - 1], `${date}`);
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-buddhist.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-buddhist.js
new file mode 100644
index 00000000000..dfec2babdf4
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-buddhist.js
@@ -0,0 +1,33 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Buddhist calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "buddhist";
+
+const cases = {
+  year2000: {
+    era: "be",
+    eraYear: 2543,
+    year: 2543,
+    month: 1,
+    monthCode: "M01",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear);
+
+  var afterWithYear = afterWithMonth.with({ year: 2220 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    2220, 1, "M01", `${name} after setting year`, inCal.era, 2220);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-coptic.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-coptic.js
new file mode 100644
index 00000000000..176ab3aa2cf
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-coptic.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Coptic calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "coptic";
+
+const cases = {
+  year2000: {
+    era: "am",
+    eraYear: 1716,
+    year: 1716,
+    month: 4,
+    monthCode: "M04",
+    calendar
+  },
+  year1: {
+    era: "am",
+    eraYear: -283,
+    year: -283,
+    month: 5,
+    monthCode: "M05",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 1917 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    1917, 1, "M01", `${name} after setting year`, inCal.era, 1917, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-ethioaa.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-ethioaa.js
new file mode 100644
index 00000000000..1c10daae253
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-ethioaa.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for ethioaa calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "ethioaa";
+
+const cases = {
+  year2000: {
+    era: "aa",
+    eraYear: 7492,
+    year: 7492,
+    month: 4,
+    monthCode: "M04",
+    calendar
+  },
+  year1: {
+    era: "aa",
+    eraYear: 5493,
+    year: 5493,
+    month: 5,
+    monthCode: "M05",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 7593 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    7593, 1, "M01", `${name} after setting year`, inCal.era, 7593, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-ethiopic.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-ethiopic.js
new file mode 100644
index 00000000000..3bcc3fa7d07
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-ethiopic.js
@@ -0,0 +1,32 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for ethiopic calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "ethiopic";
+
+const cases = {
+  year2000: {
+    era: "am",
+    eraYear: 1992,
+    month: 4,
+    monthCode: "M04",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 2220 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    2220, 1, "M01", `${name} after setting year`, inCal.era, 2220, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-gregory.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-gregory.js
new file mode 100644
index 00000000000..8a9e8594ac5
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-gregory.js
@@ -0,0 +1,39 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for gregory calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "gregory";
+
+const cases = {
+  year2000: {
+    era: "ce",
+    eraYear: 2000,
+    month: 1,
+    monthCode: "M01",
+    calendar
+  },
+  year1: {
+    era: "ce",
+    eraYear: 1,
+    month: 1,
+    monthCode: "M01",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear);
+
+  var afterWithYear = afterWithMonth.with({ year: 2220 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    2220, 1, "M01", `${name} after setting year`, inCal.era, 2220);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-hebrew.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-hebrew.js
new file mode 100644
index 00000000000..e5d4109c732
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-hebrew.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Hebrew calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "hebrew";
+
+const cases = {
+  year2000: {
+    year: 5760,
+    eraYear: 5760,
+    era: "am",
+    month: 4,
+    monthCode: "M04",
+    calendar
+  },
+  year1: {
+    year: 3761,
+    eraYear: 3761,
+    era: "am",
+    month: 4,
+    monthCode: "M04",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 5860 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    5860, 1, "M01", `${name} after setting year`, inCal.era, 5860, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-indian.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-indian.js
new file mode 100644
index 00000000000..b1e00efb62c
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-indian.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Indian calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "indian";
+
+const cases = {
+  year2000: {
+    year: 1921,
+    eraYear: 1921,
+    era: "shaka",
+    month: 10,
+    monthCode: "M10",
+    calendar
+  },
+  year1: {
+    year: -78,
+    eraYear: -78,
+    era: "shaka",
+    month: 10,
+    monthCode: "M10",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 5860 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    5860, 1, "M01", `${name} after setting year`, inCal.era, 5860, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-civil.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-civil.js
new file mode 100644
index 00000000000..95c8c330c3b
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-civil.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for islamic-civil calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "islamic-civil";
+
+const cases = {
+  year2000: {
+    year: 1420,
+    eraYear: 1420,
+    era: "ah",
+    month: 9,
+    monthCode: "M09",
+    calendar
+  },
+  year1: {
+    year: -640,
+    eraYear: 641,
+    era: "bh",
+    month: 5,
+    monthCode: "M05",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 1700 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    1700, 1, "M01", `${name} after setting year`, "ah", 1700, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-tbla.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-tbla.js
new file mode 100644
index 00000000000..043a8020a64
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-tbla.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for islamic-tbla calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "islamic-tbla";
+
+const cases = {
+  year2000: {
+    year: 1420,
+    eraYear: 1420,
+    era: "ah",
+    month: 9,
+    monthCode: "M09",
+    calendar
+  },
+  year1: {
+    year: -640,
+    eraYear: 641,
+    era: "bh",
+    month: 5,
+    monthCode: "M05",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 1700 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    1700, 1, "M01", `${name} after setting year`, "ah", 1700, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-umalqura.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-umalqura.js
new file mode 100644
index 00000000000..e730d74edd9
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-islamic-umalqura.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for islamic-umalqura calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "islamic-umalqura";
+
+const cases = {
+  year2000: {
+    year: 1420,
+    eraYear: 1420,
+    era: "ah",
+    month: 9,
+    monthCode: "M09",
+    calendar
+  },
+  year1: {
+    year: -640,
+    eraYear: 641,
+    era: "bh",
+    month: 5,
+    monthCode: "M05",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 1700 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    1700, 1, "M01", `${name} after setting year`, "ah", 1700, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-japanese.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-japanese.js
new file mode 100644
index 00000000000..d03121f3f77
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-japanese.js
@@ -0,0 +1,33 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Japanese calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "japanese";
+
+const cases = {
+  year2000: {
+    era: "heisei",
+    year: 2000,
+    eraYear: 12,
+    month: 1,
+    monthCode: "M01",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear);
+
+  var afterWithYear = afterWithMonth.with({ year: 1970 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    1970, 1, "M01", `${name} after setting year`, "showa", 45);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-persian.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-persian.js
new file mode 100644
index 00000000000..a36808dd17d
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-persian.js
@@ -0,0 +1,41 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Persian calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "persian";
+
+const cases = {
+  year2000: {
+    era: "ap",
+    year: 1378,
+    eraYear: 1378,
+    month: 10,
+    monthCode: "M10",
+    calendar
+  },
+  year1: {
+    era: "ap",
+    year: -621,
+    eraYear: -621,
+    month: 10,
+    monthCode: "M10",
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 1420 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    1420, 1, "M01", `${name} after setting year`, inCal.era, 1420, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-roc.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-roc.js
new file mode 100644
index 00000000000..b57b72462c0
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/basic-roc.js
@@ -0,0 +1,33 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for roc calendar dates
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "roc";
+
+const cases = {
+  year2000: {
+    era: "roc",
+    year: 89,
+    eraYear: 89,
+    month: 1,
+    monthCode: "M01",
+    calendar
+  },
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth,
+    inCal.year, 1, "M01", `${name} after setting month`, inCal.era, inCal.eraYear);
+
+  var afterWithYear = afterWithMonth.with({ year: 130 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear,
+    130, 1, "M01", `${name} after setting year`, inCal.era, 130);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/chinese-calendar-dates.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/chinese-calendar-dates.js
new file mode 100644
index 00000000000..0442d5e4556
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/chinese-calendar-dates.js
@@ -0,0 +1,42 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: Test `with` with Chinese calendar
+features: [Temporal]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "chinese";
+
+const cases = {
+  year2000: {
+    year: 1999,
+    month: 11,
+    monthCode: "M11",
+    calendar
+  },
+  year1900: {
+    year: 1899,
+    month: 12,
+    monthCode: "M12",
+    calendar
+  },
+  year2100: {
+    year: 2099,
+    month: 11,
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  const afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth, inCal.year, 1, "M01", `${name} (after setting month)`,
+    undefined, undefined, null);
+
+  const afterWithYear = afterWithMonth.with({ year: 2025 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear, 2025, 1, "M01", `${name} (after setting year)`,
+    undefined, undefined, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/chinese-calendar-leap-dates.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/chinese-calendar-leap-dates.js
new file mode 100644
index 00000000000..d9e6c4fb3ae
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/chinese-calendar-leap-dates.js
@@ -0,0 +1,68 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Chinese calendar leap dates
+features: [Temporal]
+---*/
+
+const calendar = "chinese";
+
+const daysInMonthCases = [
+  {
+    year: 2001,
+    leap: "M04L",
+    days: [
+      30,
+      30,
+      29,
+      30,
+      29,
+      30,
+      29,
+      29,
+      30,
+      29,
+      30,
+      29,
+      30
+    ]
+  },
+];
+for (var {year, leap, days} of daysInMonthCases) {
+  const date = Temporal.PlainYearMonth.from({
+    year,
+    month: 1,
+    calendar
+  });
+
+  const leapMonth = date.with({ monthCode: leap });
+  assert.sameValue(leapMonth.monthCode, leap);
+
+  const {monthsInYear} = date;
+
+  for (var i = monthsInYear, leapMonthIndex = undefined, monthStart = undefined; i >= 1; i--) {
+    monthStart = monthStart ? monthStart.add({ months: -1 }) : date.add({ months: monthsInYear - 1 });
+
+    const {month, monthCode, daysInMonth} = monthStart;
+    assert.sameValue(month, i);
+    assert.sameValue(daysInMonth, days[i - 1]);
+
+    if (monthCode.endsWith("L")) {
+      assert.sameValue(date.with({ monthCode }).monthCode, leap);
+      leapMonthIndex = i;
+    } else {
+      if (leapMonthIndex !== undefined && i === leapMonthIndex - 1) {
+        const inLeapMonth = monthStart.with({ monthCode: `M${ month.toString().padStart(2, "0") }L` });
+        assert.sameValue(inLeapMonth.monthCode, `${ monthCode }L`);
+      } else {
+        assert.throws(RangeError, () => monthStart.with({ monthCode: `M${ month.toString().padStart(2, "0") }L` }, { overflow: "reject" }));
+
+        if (i === 13) {
+          assert.throws(RangeError, () => monthStart.with({ monthCode: `M${ month.toString().padStart(2, "0") }L` }));
+        }
+      }
+    }
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/cross-era-boundary.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/cross-era-boundary.js
new file mode 100644
index 00000000000..3b84fc36c29
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/cross-era-boundary.js
@@ -0,0 +1,14 @@
+// Copyright (C) 2023 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: Behaviour when property bag forms a date out of bounds of the current era
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+// Last month of Showa era
+const instance = Temporal.PlainYearMonth.from({ year: 1989, month: 1, calendar: "japanese" });
+
+const result2 = instance.with({ month: 2 });
+assert.notSameValue(result2.era, instance.era, "resulting month should have crossed an era boundary");
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/dangi-calendar-dates.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/dangi-calendar-dates.js
new file mode 100644
index 00000000000..7b77d86882b
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/dangi-calendar-dates.js
@@ -0,0 +1,42 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Dangi calendar dates
+features: [Temporal]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "dangi";
+
+const cases = {
+  year2000: {
+    year: 1999,
+    month: 11,
+    monthCode: "M11",
+    calendar
+  },
+  year1900: {
+    year: 1899,
+    month: 12,
+    monthCode: "M12",
+    calendar
+  },
+  year2050: {
+    year: 2049,
+    month: 11,
+    calendar
+  }
+};
+for (var [name, result] of Object.entries(cases)) {
+  const inCal = Temporal.PlainYearMonth.from(result);
+
+  var afterWithMonth = inCal.with({ month: 1 });
+  TemporalHelpers.assertPlainYearMonth(afterWithMonth, inCal.year, 1, "M01", `${name} (after setting month)`,
+    undefined, undefined, null);
+
+  var afterWithYear = afterWithMonth.with({ year: 2025 });
+  TemporalHelpers.assertPlainYearMonth(afterWithYear, 2025, 1, "M01", `${name} (after setting year)`,
+    undefined, undefined, null);
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/dangi-calendar-leap-dates.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/dangi-calendar-leap-dates.js
new file mode 100644
index 00000000000..4ee791930fc
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/dangi-calendar-leap-dates.js
@@ -0,0 +1,68 @@
+// Copyright 2025 Google Inc, Igalia S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: with should work for Chinese calendar dates
+features: [Temporal]
+---*/
+
+const calendar = "dangi";
+
+const daysInMonthCases = [
+  {
+    year: 2001,
+    leap: "M04L",
+    days: [
+      30,
+      30,
+      30,
+      29,
+      29,
+      30,
+      29,
+      29,
+      30,
+      29,
+      30,
+      29,
+      30
+    ]
+  },
+];
+for (var {year, leap, days} of daysInMonthCases) {
+  const date = Temporal.PlainYearMonth.from({
+    year,
+    month: 1,
+    calendar
+  });
+
+  const leapMonth = date.with({ monthCode: leap });
+  assert.sameValue(leapMonth.monthCode, leap);
+
+  const {monthsInYear} = date;
+
+  for (var i = monthsInYear, leapMonthIndex = undefined, monthStart = undefined; i >= 1; i--) {
+    monthStart = monthStart ? monthStart.add({ months: -1 }) : date.add({ months: monthsInYear - 1 });
+
+    const {month, monthCode, daysInMonth} = monthStart;
+    assert.sameValue(month, i);
+    assert.sameValue(daysInMonth, days[i - 1]);
+
+    if (monthCode.endsWith("L")) {
+      assert.sameValue(date.with({ monthCode }).monthCode, leap);
+      leapMonthIndex = i;
+    } else {
+      if (leapMonthIndex !== undefined && i === leapMonthIndex - 1) {
+        const inLeapMonth = monthStart.with({ monthCode: `M${ month.toString().padStart(2, "0") }L` });
+        assert.sameValue(inLeapMonth.monthCode, `${ monthCode }L`);
+      } else {
+        assert.throws(RangeError, () => monthStart.with({ monthCode: `M${ month.toString().padStart(2, "0") }L` }, { overflow: "reject" }));
+
+        if (i === 13) {
+          assert.throws(RangeError, () => monthStart.with({ monthCode: `M${ month.toString().padStart(2, "0") }L` }));
+        }
+      }
+    }
+  }
+}
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-chinese.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-chinese.js
new file mode 100644
index 00000000000..3f5afceaf60
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-chinese.js
@@ -0,0 +1,36 @@
+// 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.with
+description: Check constraining leap months when year changes in chinese calendar
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "chinese";
+const options = { overflow: "reject" };
+const leapMonth = Temporal.PlainYearMonth.from({ year: 2017, monthCode: "M06L", calendar }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 2025 }, options),
+  2025, 7, "M06L", "month not constrained when moving to another leap year with M06L",
+  undefined, undefined, null);
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 2020 }),
+  2020, 7, "M06", "month constrained when moving to another leap year without M06L",
+  undefined, undefined, null);
+
+assert.throws(RangeError, function () {
+  leapMonth.with({ year: 2020 }, options);
+}, "reject when moving to another leap year without M06L");
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 2024 }),
+  2024, 6, "M06", "month constrained when moving to a common year",
+  undefined, undefined, null);
+
+assert.throws(RangeError, function () {
+  leapMonth.with({ year: 2024 }, options);
+}, "reject when moving to a common year");
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-dangi.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-dangi.js
new file mode 100644
index 00000000000..f4ad295c8c2
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-dangi.js
@@ -0,0 +1,36 @@
+// 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.with
+description: Check constraining leap months when year changes in dangi calendar
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "dangi";
+const options = { overflow: "reject" };
+const leapMonth = Temporal.PlainYearMonth.from({ year: 2017, monthCode: "M05L", calendar }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 2009 }, options),
+  2009, 6, "M05L", "month not constrained when moving to another leap year with M05L",
+  undefined, undefined, null);
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 2020 }),
+  2020, 6, "M05", "month constrained when moving to another leap year without M05L",
+  undefined, undefined, null);
+
+assert.throws(RangeError, function () {
+  leapMonth.with({ year: 2020 }, options);
+}, "reject when moving to another leap year without M05L");
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 2024 }),
+  2024, 5, "M05", "month constrained when moving to a common year",
+  undefined, undefined, null);
+
+assert.throws(RangeError, function () {
+  leapMonth.with({ year: 2024 }, options);
+}, "reject when moving to a common year");
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-hebrew.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-hebrew.js
new file mode 100644
index 00000000000..d03e7e1381b
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/leap-months-hebrew.js
@@ -0,0 +1,27 @@
+// 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.with
+description: Check constraining leap months when year changes in hebrew calendar
+features: [Temporal, Intl.Era-monthcode]
+includes: [temporalHelpers.js]
+---*/
+
+const calendar = "hebrew";
+const options = { overflow: "reject" };
+const leapMonth = Temporal.PlainYearMonth.from({ year: 5784, monthCode: "M05L", calendar }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 5782 }, options),
+  5782, 6, "M05L", "month not constrained when moving to another leap year",
+  "am", 5782, null);
+
+TemporalHelpers.assertPlainYearMonth(
+  leapMonth.with({ year: 5783 }),
+  5783, 6, "M06", "month constrained when moving to a common year",
+  "am", 5783, null);
+
+assert.throws(RangeError, function () {
+  leapMonth.with({ year: 5783 }, options);
+}, "reject when moving to a common year");
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-buddhist.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-buddhist.js
new file mode 100644
index 00000000000..869aca8802d
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-buddhist.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the buddhist calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 2566, monthCode: "M12", calendar: "buddhist" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  2566, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "be", /* eraYear = */ 2566
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "be", eraYear: 2560 }, options),
+  2560, 12, "M12",
+  "era and eraYear together exclude year",
+  "be", 2560
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: 2559 }, options),
+  2559, 12, "M12",
+  "year excludes era and eraYear",
+  "be", 2559
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  2566, 5, "M05",
+  "month excludes monthCode",
+  "be", 2566
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  2566, 5, "M05",
+  "monthCode excludes month",
+  "be", 2566
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 2560 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "be" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-chinese.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-chinese.js
new file mode 100644
index 00000000000..d89a66aa25c
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-chinese.js
@@ -0,0 +1,41 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the chinese calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1981, monthCode: "M12", calendar: "chinese" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1981, 12, "M12",
+  "check that all fields are as expected",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1981, 5, "M05",
+  "month excludes monthCode",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1981, 5, "M05",
+  "monthCode excludes month",
+  undefined, undefined, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 2025, era: "ce" }),
+  "eraYear and era are invalid for this calendar",
+);
+
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-coptic.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-coptic.js
new file mode 100644
index 00000000000..2dbac77256a
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-coptic.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the coptic calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1742, monthCode: "M12", calendar: "coptic" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1742, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "am", /* eraYear = */ 1742, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "am", eraYear: 1740 }, options),
+  1740, 12, "M12",
+  "era and eraYear together exclude year",
+  "am", 1740, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: 1735 }, options),
+  1735, 12, "M12",
+  "year excludes era and eraYear",
+  "am", 1735, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1742, 5, "M05",
+  "month excludes monthCode",
+  "am", 1742, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1742, 5, "M05",
+  "monthCode excludes month",
+  "am", 1742, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1741 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "am" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-dangi.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-dangi.js
new file mode 100644
index 00000000000..e5eb2a81c95
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-dangi.js
@@ -0,0 +1,41 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the dangi calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1981, monthCode: "M12", calendar: "dangi" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1981, 12, "M12",
+  "check that all fields are as expected",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1981, 5, "M05",
+  "month excludes monthCode",
+  undefined, undefined, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1981, 5, "M05",
+  "monthCode excludes month",
+  undefined, undefined, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 2025, era: "ce" }),
+  "eraYear and era are invalid for this calendar",
+);
+
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-ethioaa.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-ethioaa.js
new file mode 100644
index 00000000000..2b4feccc89d
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-ethioaa.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the ethioaa calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 7518, monthCode: "M12", calendar: "ethioaa" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  7518, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "aa", /* eraYear = */ 7518, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "aa", eraYear: 7515 }, options),
+  7515, 12, "M12",
+  "era and eraYear together exclude year",
+  "aa", 7515, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: 7510 }, options),
+  7510, 12, "M12",
+  "year excludes era and eraYear",
+  "aa", 7510, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  7518, 5, "M05",
+  "month excludes monthCode",
+  "aa", 7518, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  7518, 5, "M05",
+  "monthCode excludes month",
+  "aa", 7518, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 7512 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "aa" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-ethiopic.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-ethiopic.js
new file mode 100644
index 00000000000..626dde477ed
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-ethiopic.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the ethiopic calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 2018, monthCode: "M12", calendar: "ethiopic" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  2018, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "am", /* eraYear = */ 2018, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "aa", eraYear: 5500 }, options),
+  0, 12, "M12",
+  "era and eraYear together exclude year",
+  "aa", 5500, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: -2 }, options),
+  -2, 12, "M12",
+  "year excludes era and eraYear",
+  "aa", 5498, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  2018, 5, "M05",
+  "month excludes monthCode",
+  "am", 2018, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  2018, 5, "M05",
+  "monthCode excludes month",
+  "am", 2018, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "aa" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-gregory.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-gregory.js
new file mode 100644
index 00000000000..31113763bbc
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-gregory.js
@@ -0,0 +1,60 @@
+// Copyright (C) 2023 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: Calendar-specific mutually exclusive keys in the gregory calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1981, monthCode: "M12", calendar: "gregory" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1981, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "ce", /* eraYear = */ 1981
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "bce", eraYear: 1 }, options),
+  0, 12, "M12",
+  "era and eraYear together exclude year",
+  "bce", 1
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: -2 }, options),
+  -2, 12, "M12",
+  "year excludes era and eraYear",
+  "bce", 3
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1981, 5, "M05",
+  "month excludes monthCode",
+  "ce", 1981
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1981, 5, "M05",
+  "monthCode excludes month",
+  "ce", 1981
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "bce" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-hebrew.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-hebrew.js
new file mode 100644
index 00000000000..0a42e09572d
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-hebrew.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the hebrew calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 5786, monthCode: "M12", calendar: "hebrew" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  5786, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "am", /* eraYear = */ 5786, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "am", eraYear: 5760 }, options),
+  5760, 13, "M12",
+  "era and eraYear together exclude year",
+  "am", 5760, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: 5784 }, options),
+  5784, 13, "M12",
+  "year excludes era and eraYear",
+  "am", 5784, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  5786, 5, "M05",
+  "month excludes monthCode",
+  "am", 5786, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  5786, 5, "M05",
+  "monthCode excludes month",
+  "am", 5786, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 2560 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "am" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-indian.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-indian.js
new file mode 100644
index 00000000000..7f027bcf8b7
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-indian.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the indian calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1947, monthCode: "M12", calendar: "indian" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1947, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "shaka", /* eraYear = */ 1947, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "shaka", eraYear: 1940 }, options),
+  1940, 12, "M12",
+  "era and eraYear together exclude year",
+  "shaka", 1940, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: 1943 }, options),
+  1943, 12, "M12",
+  "year excludes era and eraYear",
+  "shaka", 1943, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1947, 5, "M05",
+  "month excludes monthCode",
+  "shaka", 1947, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1947, 5, "M05",
+  "monthCode excludes month",
+  "shaka", 1947, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1940 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "shaka" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-civil.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-civil.js
new file mode 100644
index 00000000000..45f66031eb3
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-civil.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the islamic-civil calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1447, monthCode: "M12", calendar: "islamic-civil" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1447, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "ah", /* eraYear = */ 1447, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "bh", eraYear: 1 }, options),
+  0, 12, "M12",
+  "era and eraYear together exclude year",
+  "bh", 1, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: -2 }, options),
+  -2, 12, "M12",
+  "year excludes era and eraYear",
+  "bh", 3, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1447, 5, "M05",
+  "month excludes monthCode",
+  "ah", 1447, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1447, 5, "M05",
+  "monthCode excludes month",
+  "ah", 1447, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "bh" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-tbla.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-tbla.js
new file mode 100644
index 00000000000..7a993aee0c0
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-tbla.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the islamic-tbla calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1447, monthCode: "M12", calendar: "islamic-tbla" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1447, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "ah", /* eraYear = */ 1447, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "bh", eraYear: 1 }, options),
+  0, 12, "M12",
+  "era and eraYear together exclude year",
+  "bh", 1, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: -2 }, options),
+  -2, 12, "M12",
+  "year excludes era and eraYear",
+  "bh", 3, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1447, 5, "M05",
+  "month excludes monthCode",
+  "ah", 1447, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1447, 5, "M05",
+  "monthCode excludes month",
+  "ah", 1447, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "bh" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-umalqura.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-umalqura.js
new file mode 100644
index 00000000000..ea5b0306abe
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-islamic-umalqura.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the islamic-umalqura calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1447, monthCode: "M12", calendar: "islamic-umalqura" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1447, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "ah", /* eraYear = */ 1447, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "bh", eraYear: 1 }, options),
+  0, 12, "M12",
+  "era and eraYear together exclude year",
+  "bh", 1, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: -2 }, options),
+  -2, 12, "M12",
+  "year excludes era and eraYear",
+  "bh", 3, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1447, 5, "M05",
+  "month excludes monthCode",
+  "ah", 1447, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1447, 5, "M05",
+  "monthCode excludes month",
+  "ah", 1447, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "bh" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-japanese.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-japanese.js
new file mode 100644
index 00000000000..620f397f16b
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-japanese.js
@@ -0,0 +1,60 @@
+// Copyright (C) 2023 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.with
+description: Calendar-specific mutually exclusive keys in the japanese calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const lastDayOfShowa = Temporal.PlainYearMonth.from({ era: "showa", eraYear: 64, year: 1989, month: 1, monthCode: "M01", calendar: "japanese" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  lastDayOfShowa,
+  1989, 1, "M01",
+  "check expected fields",
+  /* era = */ "showa", /* eraYear = */ 64
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  lastDayOfShowa.with({ month: 2 }, options),
+  1989, 2, "M02",
+  "month excludes monthCode, era, and eraYear",
+  "heisei", 1
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  lastDayOfShowa.with({ monthCode: "M03" }, options),
+  1989, 3, "M03",
+  "monthCode excludes month, era, and eraYear",
+  "heisei", 1
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  lastDayOfShowa.with({ year: 1988 }, options),
+  1988, 1, "M01",
+  "year excludes era and eraYear (within same era)",
+  "showa", 63
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  lastDayOfShowa.with({ year: 1990 }, options),
+  1990, 1, "M01",
+  "year excludes era and eraYear (in a different era)",
+  "heisei", 2
+);
+
+assert.throws(
+  TypeError,
+  () => lastDayOfShowa.with({ eraYear: 1 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => lastDayOfShowa.with({ era: "heisei" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-persian.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-persian.js
new file mode 100644
index 00000000000..3b1559d4d0f
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-persian.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the persian calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 1404, monthCode: "M12", calendar: "persian" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  1404, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "ap", /* eraYear = */ 1404, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "ap", eraYear: 1400 }, options),
+  1400, 12, "M12",
+  "era and eraYear together exclude year",
+  "ap", 1400, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: 1402 }, options),
+  1402, 12, "M12",
+  "year excludes era and eraYear",
+  "ap", 1402, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  1404, 5, "M05",
+  "month excludes monthCode",
+  "ap", 1404, null
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  1404, 5, "M05",
+  "monthCode excludes month",
+  "ap", 1404, null
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1403 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "ap" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);
diff --git a/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-roc.js b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-roc.js
new file mode 100644
index 00000000000..170dd0f39b4
--- /dev/null
+++ b/test/intl402/Temporal/PlainYearMonth/prototype/with/mutually-exclusive-fields-roc.js
@@ -0,0 +1,60 @@
+// 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.with
+description: Calendar-specific mutually exclusive keys in the roc calendar
+info: NonIsoFieldKeysToIgnore ( _calendar_, _keys_ )
+includes: [temporalHelpers.js]
+features: [Temporal, Intl.Era-monthcode]
+---*/
+
+const options = { overflow: "reject" };
+const instance = Temporal.PlainYearMonth.from({ year: 114, monthCode: "M12", calendar: "roc" }, options);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance,
+  114, 12, "M12",
+  "check that all fields are as expected",
+  /* era = */ "roc", /* eraYear = */ 114
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ era: "broc", eraYear: 1 }, options),
+  0, 12, "M12",
+  "era and eraYear together exclude year",
+  "broc", 1
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ year: -2 }, options),
+  -2, 12, "M12",
+  "year excludes era and eraYear",
+  "broc", 3
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ month: 5 }, options),
+  114, 5, "M05",
+  "month excludes monthCode",
+  "roc", 114
+);
+
+TemporalHelpers.assertPlainYearMonth(
+  instance.with({ monthCode: "M05" }, options),
+  114, 5, "M05",
+  "monthCode excludes month",
+  "roc", 114
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ eraYear: 1 }),
+  "eraYear excludes year and era, and cannot be provided without era",
+);
+
+assert.throws(
+  TypeError,
+  () => instance.with({ era: "broc" }),
+  "era excludes year and eraYear, and cannot be provided without eraYear",
+);