Temporal: Expand ISO8601 PlainDate.p.with tests

Move coverage of plural units to a separate file, and add some more
coverage for the overflow option.

test/built-ins/Temporal/PlainDate/prototype/with/basic.js

@@ -21,8 +21,3 @@ TemporalHelpers.assertPlainDate(withMonthCode, 1976, 5, "M05", 18, "with(monthCo
 
 const withDay = plainDate.with({ day: 17 });
 TemporalHelpers.assertPlainDate(withDay, 1976, 11, "M11", 17, "with(day)");
-
-const withPlural = plainDate.with({ months: 12, day: 15 });
-TemporalHelpers.assertPlainDate(withPlural, 1976, 11, "M11", 15, "with(plural)");
-
-assert.throws(RangeError, () => plainDate.with({ month: 5, monthCode: 'M06' }));

test/built-ins/Temporal/PlainDate/prototype/with/overflow.js

@@ -0,0 +1,59 @@
+// Copyright (C) 2025 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindate.prototype.with
+description: Basic tests for the overflow option
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const date = new Temporal.PlainDate(1976, 11, 18);
+
+assert.throws(
+  RangeError,
+  () => date.with({ year: -300000 }),
+  "too-low year rejects even with overflow constrain");
+
+assert.throws(
+  RangeError,
+  () => date.with({ year: 300000 }),
+  "too-high year rejects even with overflow constrain");
+
+assert.throws(
+  RangeError,
+  () => date.with({ month: 0 }),
+  "non-positive month rejects even with overflow constrain");
+
+TemporalHelpers.assertPlainDate(
+  date.with({ month: 13 }),
+  1976, 12, "M12", 18,
+  "too-high month is constrained to highest value");
+
+assert.throws(RangeError, function () {
+  date.with({ month: 13 }, { overflow: "reject" });
+}, "too-high month rejects");
+
+assert.throws(
+  RangeError,
+  () => date.with({ monthCode: "M13" }),
+  "Invalid monthCode for calendar rejects even with overflow constrain");
+
+assert.throws(
+  RangeError,
+  () => date.with({ day: 0 }),
+  "non-positive day rejects even with overflow constrain");
+
+TemporalHelpers.assertPlainDate(
+  date.with({ day: 31 }),
+  1976, 11, "M11", 30,
+  "too-high day is constrained to highest value");
+
+assert.throws(RangeError, function () {
+  date.with({ day: 31 }, { overflow: "reject" });
+}, "too-high day rejects");
+
+assert.throws(
+  RangeError,
+  () => date.with({ month: 5, monthCode: "M06" }),
+  "Conflicting month and monthCode rejects even with overflow constrain");

test/built-ins/Temporal/PlainDate/prototype/with/plural-units-ignored.js

@@ -0,0 +1,14 @@
+// Copyright (C) 2021 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindate.prototype.with
+description: Plural units are not valid in the property bag
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const plainDate = new Temporal.PlainDate(1976, 11, 18);
+
+const withPlural = plainDate.with({ months: 12, day: 15 });
+TemporalHelpers.assertPlainDate(withPlural, 1976, 11, "M11", 15, "Plural units in the property bag should ignored");