From bb8349792dbaa167fee3f242a1c1c8602a577c40 Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Tue, 4 Nov 2025 15:04:28 -0800
Subject: [PATCH 1/7] Temporal: Add test for formatting Temporal objects with
 era formatter

See https://github.com/tc39/proposal-temporal/issues/3049
---
 .../temporal-objects-format-with-era.js       | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js

diff --git a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
new file mode 100644
index 00000000000..4525d09be3b
--- /dev/null
+++ b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
@@ -0,0 +1,19 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-datetime-format-functions
+description: >
+  If era option and no other options are provided to DateTimeFormat constructor,
+  objects should be formatted with default options
+features: [Temporal]
+---*/
+
+const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+
+assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
+assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
+assert(formatter.format(new Temporal.PlainMonthDay(11, 4, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
+assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("A"), "formatting a PlainTime should work");
+assert(formatter.format(new Temporal.PlainDateTime(2025, 11, 4, 14, 46)).startsWith("11"), "formatting a PlainDateTime should work");
+assert(formatter.format(new Temporal.Instant(0n)).startsWith("12"), "formatting an Instant should work");

From cf569dedc62e9585221dda00bb1852c9a05a0b61 Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Fri, 7 Nov 2025 12:44:13 -0800
Subject: [PATCH 2/7] Be consistent with spec about not including era when
 formatting a PlainTime

---
 .../prototype/format/temporal-objects-format-with-era.js        | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
index 4525d09be3b..bcea2b9a2ff 100644
--- a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
@@ -14,6 +14,6 @@ const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
 assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
 assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
 assert(formatter.format(new Temporal.PlainMonthDay(11, 4, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
-assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("A"), "formatting a PlainTime should work");
+assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("2"), "formatting a PlainTime should work");
 assert(formatter.format(new Temporal.PlainDateTime(2025, 11, 4, 14, 46)).startsWith("11"), "formatting a PlainDateTime should work");
 assert(formatter.format(new Temporal.Instant(0n)).startsWith("12"), "formatting an Instant should work");

From 561c6713d5c1c89799f808fd9a5b9bbeb7c9fd6c Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Fri, 7 Nov 2025 12:44:18 -0800
Subject: [PATCH 3/7] Add more tests

---
 .../Instant/prototype/toLocaleString/era.js   | 14 ++++++++++
 .../PlainDate/prototype/toLocaleString/era.js | 14 ++++++++++
 .../prototype/toLocaleString/era.js           | 14 ++++++++++
 .../prototype/toLocaleString/era.js           | 14 ++++++++++
 .../PlainTime/prototype/toLocaleString/era.js | 17 +++++++++++
 .../prototype/toLocaleString/era.js           | 14 ++++++++++
 .../prototype/toLocaleString/era.js           | 14 ++++++++++
 .../temporal-objects-format-with-era.js       | 19 +++++++++++++
 .../temporal-objects-format-with-era.js       | 28 +++++++++++++++++++
 .../temporal-objects-format-with-era.js       | 27 ++++++++++++++++++
 10 files changed, 175 insertions(+)
 create mode 100644 test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
 create mode 100644 test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
 create mode 100644 test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
 create mode 100644 test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
 create mode 100644 test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
 create mode 100644 test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
 create mode 100644 test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
 create mode 100644 test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
 create mode 100644 test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
 create mode 100644 test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js

diff --git a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
new file mode 100644
index 00000000000..90cf1eb651e
--- /dev/null
+++ b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
@@ -0,0 +1,14 @@
+// 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.instant.prototype.tolocalestring
+description: >
+    If era option and no other options are provided to toLocaleString,
+    Instant should be foramtted with default options
+features: [Temporal]
+---*/
+
+const instant = new Temporal.Instant(0n);
+
+assert(instant.toLocaleString("en", { era: "narrow" }).startsWith("1"), "toLocaleString on an Instant with era option should work");
diff --git a/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
new file mode 100644
index 00000000000..9e0cfd5f311
--- /dev/null
+++ b/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
@@ -0,0 +1,14 @@
+// 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.tolocalestring
+description: >
+    If era option and no other options are provided to toLocaleString,
+    PlainDate should be foramtted with default options
+features: [Temporal]
+---*/
+
+const date = new Temporal.PlainDate(2000, 5, 2, "gregory");
+
+assert(date.toLocaleString("en", { era: "narrow" }).startsWith("5"), "toLocaleString on a PlainDate with era option should work");
diff --git a/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
new file mode 100644
index 00000000000..60793f496c5
--- /dev/null
+++ b/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
@@ -0,0 +1,14 @@
+// Copyright (C) 2025 Igalia, S.L.. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plaindatetime.prototype.tolocalestring
+description: >
+    If era option and no other options are provided to toLocaleString,
+    PlainDateTime should be foramtted with default options
+features: [Temporal]
+---*/
+
+date = new Temporal.PlainDateTime(2000, 5, 2, 14, 46, 0, 0, 0, 0, "gregory");
+
+assert(date.toLocaleString("en", { era: "narrow" }).startsWith("5"), "toLocaleString on a PlainDateTime with era option should work");
diff --git a/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
new file mode 100644
index 00000000000..468339a115b
--- /dev/null
+++ b/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
@@ -0,0 +1,14 @@
+// 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.plainmonthday.prototype.tolocalestring
+description: >
+    If era option and no other options are provided to toLocaleString,
+    PlainMonthDay should be foramtted with default options
+features: [Temporal]
+---*/
+
+const date = new Temporal.PlainMonthDay(5, 2, "gregory");
+
+assert(date.toLocaleString("en", { era: "narrow" }).startsWith("5"), "toLocaleString on a PlainMonthDay with era option should work");
diff --git a/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
new file mode 100644
index 00000000000..ca0c78fd522
--- /dev/null
+++ b/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
@@ -0,0 +1,17 @@
+// 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.plaintime.prototype.tolocalestring
+description: >
+    If era option and no other options are provided to toLocaleString,
+    PlainTime should be foramtted with default options
+features: [Temporal]
+---*/
+
+const date = new Temporal.PlainTime(14, 46);
+
+const result = date.toLocaleString("en", { era: "narrow" });
+
+assert(result.startsWith("2"), "toLocaleString on a PlainTime with era option should work");
+assert(!result.includes("A"), "era should be ignored when formatting a PlainTime");
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
new file mode 100644
index 00000000000..446f6e5a527
--- /dev/null
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
@@ -0,0 +1,14 @@
+// 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.tolocalestring
+description: >
+    If era option and no other options are provided to toLocaleString,
+    PlainYearMonth should be foramtted with default options
+features: [Temporal]
+---*/
+
+const date = new Temporal.PlainYearMonth(2000, 5, "gregory");
+
+assert(date.toLocaleString("en", { era: "narrow" }).startsWith("5"), "toLocaleString on a PlainYearMonth with era option should work");
diff --git a/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
new file mode 100644
index 00000000000..f91fabd0806
--- /dev/null
+++ b/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
@@ -0,0 +1,14 @@
+// Copyright (C) 2025 Igalia, S.L.. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.zoneddatetime.prototype.tolocalestring
+description: >
+    If era option and no other options are provided to toLocaleString,
+    ZonedDateTime should be foramtted with default options
+features: [Temporal]
+---*/
+
+const zdt = new Temporal.ZonedDateTime(0n, "UTC");
+
+assert(zdt.toLocaleString("en", { era: "narrow" }).startsWith("1"), "toLocaleString on a ZonedDateTime with era option should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
new file mode 100644
index 00000000000..e6b05007d60
--- /dev/null
+++ b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
@@ -0,0 +1,19 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-datetime-format-functions
+description: >
+  If era option and no other options are provided to DateTimeFormat constructor,
+  objects should be formatted with default options
+features: [Temporal]
+---*/
+
+const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+
+assert(formatter.formatRange(new Temporal.PlainDate(2025, 11, 4), new Temporal.PlainDate(2025, 11, 5)).startsWith("11"), "formatting a PlainDate should work");
+assert(formatter.formatRange(new Temporal.PlainYearMonth(2025, 11, "gregory"), new Temporal.PlainYearMonth(2025, 12, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
+assert(formatter.formatRange(new Temporal.PlainMonthDay(11, 4, "gregory"), new Temporal.PlainMonthDay(11, 14, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
+assert(formatter.formatRange(new Temporal.PlainTime(14, 46), new Temporal.PlainTime(17, 46)).startsWith("2"), "formatting a PlainTime should work");
+assert(formatter.formatRange(new Temporal.PlainDateTime(2025, 11, 4, 14, 46), new Temporal.PlainDateTime(2025, 11, 15, 14, 47)).startsWith("11"), "formatting a PlainDateTime should work");
+assert(formatter.formatRange(new Temporal.Instant(0n), new Temporal.Instant(1000000000n)).startsWith("12"), "formatting an Instant should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
new file mode 100644
index 00000000000..b66427494f9
--- /dev/null
+++ b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
@@ -0,0 +1,28 @@
+// Copyright (C) 2024 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-datetime-format-functions
+description: >
+  If era option and no other options are provided to DateTimeFormat constructor,
+  objects should be formatted with default options
+features: [Temporal]
+---*/
+
+const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+
+function checkEra(parts) {
+    for (let part of parts) {
+        if (part.type === 'era' && part.value.startsWith('A'))
+            return true;
+    }
+    return false;
+}
+
+assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDate(2025, 11, 4), new Temporal.PlainDate(2025, 11, 5))), "formatting a PlainDate should work");
+assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDate(2025, 11, 4), new Temporal.PlainDate(2025, 11, 5))), "formatting a PlainDate should work");
+assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainYearMonth(2025, 11, "gregory"), new Temporal.PlainYearMonth(2025, 12, "gregory"))), "formatting a PlainYearMonth should work");
+assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainMonthDay(11, 4, "gregory"), new Temporal.PlainMonthDay(11, 14, "gregory"))), "formatting a PlainMonthDay should work");
+assert(!checkEra(formatter.formatRangeToParts(new Temporal.PlainTime(14, 46), new Temporal.PlainTime(17, 46))), "formatting a PlainTime should work");
+assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDateTime(2025, 11, 4, 14, 46), new Temporal.PlainDateTime(2025, 11, 15, 14, 47))), "formatting a PlainDateTime should work");
+assert(checkEra(formatter.formatRangeToParts(new Temporal.Instant(0n), new Temporal.Instant(1000000000n))), "formatting an Instant should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
new file mode 100644
index 00000000000..9bbd79ad87c
--- /dev/null
+++ b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.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-datetime-format-functions
+description: >
+  If era option and no other options are provided to DateTimeFormat constructor,
+  objects should be formatted with default options
+features: [Temporal]
+---*/
+
+const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+
+function checkEra(parts) {
+    for (let part of parts) {
+        if (part.type === 'era' && part.value.startsWith('A'))
+            return true;
+    }
+    return false;
+}
+
+assert(checkEra(formatter.formatToParts(new Temporal.PlainDate(2025, 11, 4))), "formatting a PlainDate should work");
+assert(checkEra(formatter.formatToParts(new Temporal.PlainYearMonth(2025, 11, "gregory"))), "formatting a PlainYearMonth should work");
+assert(checkEra(formatter.formatToParts(new Temporal.PlainMonthDay(11, 4, "gregory"))), "formatting a PlainMonthDay should work");
+assert(!checkEra(formatter.formatToParts(new Temporal.PlainTime(14, 46))), "formatting a PlainTime should work");
+assert(checkEra(formatter.formatToParts(new Temporal.PlainDateTime(2025, 11, 4, 14, 46))), "formatting a PlainDateTime should work");
+assert(checkEra(formatter.formatToParts(new Temporal.Instant(0n))), "formatting an Instant should work");

From 8ae6c6275539d863398cc89d86fc478ea78db52b Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Fri, 7 Nov 2025 12:57:49 -0800
Subject: [PATCH 4/7] Fix locales

---
 .../Instant/prototype/toLocaleString/era.js       |  1 +
 .../PlainDate/prototype/toLocaleString/era.js     |  1 +
 .../PlainDateTime/prototype/toLocaleString/era.js |  1 +
 .../PlainMonthDay/prototype/toLocaleString/era.js |  1 +
 .../PlainTime/prototype/toLocaleString/era.js     |  1 +
 .../prototype/toLocaleString/era.js               |  1 +
 .../ZonedDateTime/prototype/toLocaleString/era.js |  1 +
 .../format/temporal-objects-format-with-era.js    |  3 ++-
 .../temporal-objects-format-with-era.js           | 15 ++++++++-------
 .../temporal-objects-format-with-era.js           |  3 ++-
 .../temporal-objects-format-with-era.js           |  3 ++-
 11 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
index 90cf1eb651e..2a2c394a832 100644
--- a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
@@ -7,6 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     Instant should be foramtted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
 const instant = new Temporal.Instant(0n);
diff --git a/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
index 9e0cfd5f311..3719bdcf559 100644
--- a/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
@@ -7,6 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainDate should be foramtted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
 const date = new Temporal.PlainDate(2000, 5, 2, "gregory");
diff --git a/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
index 60793f496c5..b2c986e00b3 100644
--- a/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
@@ -7,6 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainDateTime should be foramtted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
 date = new Temporal.PlainDateTime(2000, 5, 2, 14, 46, 0, 0, 0, 0, "gregory");
diff --git a/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
index 468339a115b..7c00c8d893c 100644
--- a/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
@@ -7,6 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainMonthDay should be foramtted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
 const date = new Temporal.PlainMonthDay(5, 2, "gregory");
diff --git a/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
index ca0c78fd522..52a547d595d 100644
--- a/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
@@ -7,6 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainTime should be foramtted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
 const date = new Temporal.PlainTime(14, 46);
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
index 446f6e5a527..d19d28ce73a 100644
--- a/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
@@ -7,6 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainYearMonth should be foramtted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
 const date = new Temporal.PlainYearMonth(2000, 5, "gregory");
diff --git a/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
index f91fabd0806..cc41ffc8954 100644
--- a/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
@@ -7,6 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     ZonedDateTime should be foramtted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
 const zdt = new Temporal.ZonedDateTime(0n, "UTC");
diff --git a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
index bcea2b9a2ff..03d0d91228a 100644
--- a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
@@ -7,9 +7,10 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
 
 assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
 assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
index e6b05007d60..03d0d91228a 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
@@ -7,13 +7,14 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
 
-assert(formatter.formatRange(new Temporal.PlainDate(2025, 11, 4), new Temporal.PlainDate(2025, 11, 5)).startsWith("11"), "formatting a PlainDate should work");
-assert(formatter.formatRange(new Temporal.PlainYearMonth(2025, 11, "gregory"), new Temporal.PlainYearMonth(2025, 12, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
-assert(formatter.formatRange(new Temporal.PlainMonthDay(11, 4, "gregory"), new Temporal.PlainMonthDay(11, 14, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
-assert(formatter.formatRange(new Temporal.PlainTime(14, 46), new Temporal.PlainTime(17, 46)).startsWith("2"), "formatting a PlainTime should work");
-assert(formatter.formatRange(new Temporal.PlainDateTime(2025, 11, 4, 14, 46), new Temporal.PlainDateTime(2025, 11, 15, 14, 47)).startsWith("11"), "formatting a PlainDateTime should work");
-assert(formatter.formatRange(new Temporal.Instant(0n), new Temporal.Instant(1000000000n)).startsWith("12"), "formatting an Instant should work");
+assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
+assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
+assert(formatter.format(new Temporal.PlainMonthDay(11, 4, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
+assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("2"), "formatting a PlainTime should work");
+assert(formatter.format(new Temporal.PlainDateTime(2025, 11, 4, 14, 46)).startsWith("11"), "formatting a PlainDateTime should work");
+assert(formatter.format(new Temporal.Instant(0n)).startsWith("12"), "formatting an Instant should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
index b66427494f9..a8758568811 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
@@ -7,9 +7,10 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
 
 function checkEra(parts) {
     for (let part of parts) {
diff --git a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
index 9bbd79ad87c..f4a0763ab4c 100644
--- a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
@@ -7,9 +7,10 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
+locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat([], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
 
 function checkEra(parts) {
     for (let part of parts) {

From 28e653d28d985bea3622b15f9ea8d96ea6ae79f6 Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Fri, 7 Nov 2025 13:02:34 -0800
Subject: [PATCH 5/7] Pass explicit time zones

---
 .../Temporal/Instant/prototype/toLocaleString/era.js          | 2 +-
 .../prototype/format/temporal-objects-format-with-era.js      | 4 ++--
 .../prototype/formatRange/temporal-objects-format-with-era.js | 4 ++--
 .../formatRangeToParts/temporal-objects-format-with-era.js    | 2 +-
 .../formatToParts/temporal-objects-format-with-era.js         | 2 +-
 5 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
index 2a2c394a832..1618764681f 100644
--- a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
@@ -12,4 +12,4 @@ locales: [en]
 
 const instant = new Temporal.Instant(0n);
 
-assert(instant.toLocaleString("en", { era: "narrow" }).startsWith("1"), "toLocaleString on an Instant with era option should work");
+assert(instant.toLocaleString("en", { era: "narrow", timeZone: "UTC" }).startsWith("1"), "toLocaleString on an Instant with era option should work");
diff --git a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
index 03d0d91228a..4cf269eb835 100644
--- a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
@@ -10,11 +10,11 @@ features: [Temporal]
 locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
 
 assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
 assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
 assert(formatter.format(new Temporal.PlainMonthDay(11, 4, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
 assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("2"), "formatting a PlainTime should work");
 assert(formatter.format(new Temporal.PlainDateTime(2025, 11, 4, 14, 46)).startsWith("11"), "formatting a PlainDateTime should work");
-assert(formatter.format(new Temporal.Instant(0n)).startsWith("12"), "formatting an Instant should work");
+assert(formatter.format(new Temporal.Instant(0n)).startsWith("1"), "formatting an Instant should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
index 03d0d91228a..4cf269eb835 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
@@ -10,11 +10,11 @@ features: [Temporal]
 locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
 
 assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
 assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
 assert(formatter.format(new Temporal.PlainMonthDay(11, 4, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
 assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("2"), "formatting a PlainTime should work");
 assert(formatter.format(new Temporal.PlainDateTime(2025, 11, 4, 14, 46)).startsWith("11"), "formatting a PlainDateTime should work");
-assert(formatter.format(new Temporal.Instant(0n)).startsWith("12"), "formatting an Instant should work");
+assert(formatter.format(new Temporal.Instant(0n)).startsWith("1"), "formatting an Instant should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
index a8758568811..bc3aead80c7 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
@@ -10,7 +10,7 @@ features: [Temporal]
 locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
 
 function checkEra(parts) {
     for (let part of parts) {
diff --git a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
index f4a0763ab4c..4a8b3bfbeb1 100644
--- a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
@@ -10,7 +10,7 @@ features: [Temporal]
 locales: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
 
 function checkEra(parts) {
     for (let part of parts) {

From bd540ad97673d99d15728af767fe7e3f940bd445 Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Fri, 7 Nov 2025 13:09:08 -0800
Subject: [PATCH 6/7] Fix locales again

---
 test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js | 2 +-
 .../Temporal/PlainDate/prototype/toLocaleString/era.js          | 2 +-
 .../Temporal/PlainDateTime/prototype/toLocaleString/era.js      | 2 +-
 .../Temporal/PlainMonthDay/prototype/toLocaleString/era.js      | 2 +-
 .../Temporal/PlainTime/prototype/toLocaleString/era.js          | 2 +-
 .../Temporal/PlainYearMonth/prototype/toLocaleString/era.js     | 2 +-
 .../Temporal/ZonedDateTime/prototype/toLocaleString/era.js      | 2 +-
 .../prototype/format/temporal-objects-format-with-era.js        | 2 +-
 .../prototype/formatRange/temporal-objects-format-with-era.js   | 2 +-
 .../formatRangeToParts/temporal-objects-format-with-era.js      | 2 +-
 .../prototype/formatToParts/temporal-objects-format-with-era.js | 2 +-
 11 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
index 1618764681f..6daee3deec3 100644
--- a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
@@ -7,7 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     Instant should be foramtted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const instant = new Temporal.Instant(0n);
diff --git a/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
index 3719bdcf559..d6ab1e8fd96 100644
--- a/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainDate/prototype/toLocaleString/era.js
@@ -7,7 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainDate should be foramtted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const date = new Temporal.PlainDate(2000, 5, 2, "gregory");
diff --git a/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
index b2c986e00b3..eace04aed87 100644
--- a/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainDateTime/prototype/toLocaleString/era.js
@@ -7,7 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainDateTime should be foramtted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 date = new Temporal.PlainDateTime(2000, 5, 2, 14, 46, 0, 0, 0, 0, "gregory");
diff --git a/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
index 7c00c8d893c..d4f51b418ab 100644
--- a/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainMonthDay/prototype/toLocaleString/era.js
@@ -7,7 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainMonthDay should be foramtted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const date = new Temporal.PlainMonthDay(5, 2, "gregory");
diff --git a/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
index 52a547d595d..7f5b59fa3b4 100644
--- a/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainTime/prototype/toLocaleString/era.js
@@ -7,7 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainTime should be foramtted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const date = new Temporal.PlainTime(14, 46);
diff --git a/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
index d19d28ce73a..7fe4beece1b 100644
--- a/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/PlainYearMonth/prototype/toLocaleString/era.js
@@ -7,7 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     PlainYearMonth should be foramtted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const date = new Temporal.PlainYearMonth(2000, 5, "gregory");
diff --git a/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js b/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
index cc41ffc8954..1495c9b62a3 100644
--- a/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/ZonedDateTime/prototype/toLocaleString/era.js
@@ -7,7 +7,7 @@ description: >
     If era option and no other options are provided to toLocaleString,
     ZonedDateTime should be foramtted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const zdt = new Temporal.ZonedDateTime(0n, "UTC");
diff --git a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
index 4cf269eb835..be3ebcd96c1 100644
--- a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
@@ -7,7 +7,7 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
diff --git a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
index 4cf269eb835..be3ebcd96c1 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
@@ -7,7 +7,7 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
diff --git a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
index bc3aead80c7..15762a93c4b 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
@@ -7,7 +7,7 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
diff --git a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
index 4a8b3bfbeb1..8ae3eb48b13 100644
--- a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
@@ -7,7 +7,7 @@ description: >
   If era option and no other options are provided to DateTimeFormat constructor,
   objects should be formatted with default options
 features: [Temporal]
-locales: [en]
+locale: [en]
 ---*/
 
 const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });

From eb7cd3f84fc20fccc37bbfd906dff942ea734541 Mon Sep 17 00:00:00 2001
From: Tim Chevalier <tjc@igalia.com>
Date: Mon, 10 Nov 2025 12:24:56 -0800
Subject: [PATCH 7/7] Remove time zone options

---
 .../Instant/prototype/toLocaleString/era.js     |  4 +++-
 .../format/temporal-objects-format-with-era.js  |  5 +++--
 .../temporal-objects-format-with-era.js         | 17 +++++++++++------
 .../temporal-objects-format-with-era.js         |  7 +++----
 .../temporal-objects-format-with-era.js         |  2 +-
 5 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
index 6daee3deec3..4978a0441d3 100644
--- a/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
+++ b/test/built-ins/Temporal/Instant/prototype/toLocaleString/era.js
@@ -12,4 +12,6 @@ locale: [en]
 
 const instant = new Temporal.Instant(0n);
 
-assert(instant.toLocaleString("en", { era: "narrow", timeZone: "UTC" }).startsWith("1"), "toLocaleString on an Instant with era option should work");
+const instantResult = instant.toLocaleString("en", { era: "narrow" });
+const dateResult = new Date(0).toLocaleString(["en"], { era: "narrow" });
+assert.sameValue(instantResult, dateResult, "toLocaleString on an Instant with era option should return the same results as toLocaleString on the same Date with the same options");
diff --git a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
index be3ebcd96c1..5d889e3478f 100644
--- a/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/format/temporal-objects-format-with-era.js
@@ -10,11 +10,12 @@ features: [Temporal]
 locale: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
 
 assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
 assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
 assert(formatter.format(new Temporal.PlainMonthDay(11, 4, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
 assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("2"), "formatting a PlainTime should work");
 assert(formatter.format(new Temporal.PlainDateTime(2025, 11, 4, 14, 46)).startsWith("11"), "formatting a PlainDateTime should work");
-assert(formatter.format(new Temporal.Instant(0n)).startsWith("1"), "formatting an Instant should work");
+assert.sameValue(formatter.format(new Temporal.Instant(0n)),
+                 new Date(0).toLocaleString(["en"], { era: "narrow" }), "toLocaleString on an Instant with era option should return the same results as toLocaleString on the same Date with the same options");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
index be3ebcd96c1..3a79a6e64cf 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRange/temporal-objects-format-with-era.js
@@ -12,9 +12,14 @@ locale: [en]
 
 const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
 
-assert(formatter.format(new Temporal.PlainDate(2025, 11, 4)).startsWith("11"), "formatting a PlainDate should work");
-assert(formatter.format(new Temporal.PlainYearMonth(2025, 11, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
-assert(formatter.format(new Temporal.PlainMonthDay(11, 4, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
-assert(formatter.format(new Temporal.PlainTime(14, 46)).startsWith("2"), "formatting a PlainTime should work");
-assert(formatter.format(new Temporal.PlainDateTime(2025, 11, 4, 14, 46)).startsWith("11"), "formatting a PlainDateTime should work");
-assert(formatter.format(new Temporal.Instant(0n)).startsWith("1"), "formatting an Instant should work");
+assert(formatter.formatRange(new Temporal.PlainDate(2025, 11, 4), new Temporal.PlainDate(2025, 11, 5)).startsWith("11"), "formatting a PlainDate should work");
+assert(formatter.formatRange(new Temporal.PlainYearMonth(2025, 11, "gregory"), new Temporal.PlainYearMonth(2025, 12, "gregory")).startsWith("11"), "formatting a PlainYearMonth should work");
+assert(formatter.formatRange(new Temporal.PlainMonthDay(11, 4, "gregory"), new Temporal.PlainMonthDay(11, 14, "gregory")).startsWith("11"), "formatting a PlainMonthDay should work");
+assert(formatter.formatRange(new Temporal.PlainTime(14, 46), new Temporal.PlainTime(17, 46)).startsWith("2"), "formatting a PlainTime should work");
+assert(formatter.formatRange(new Temporal.PlainDateTime(2025, 11, 4, 14, 16, 0, 0, 0, 0, "gregory"), new Temporal.PlainDateTime(2025, 11, 15, 14, 47, 0, 0, 0, 0, "gregory")).startsWith("11"), "formatting a PlainDateTime should work");
+
+// For instants, check the output of formatRange on the equivalent Dates and then check that this is a prefix
+// of the output of formatRange on the Instants, because the time zone of the host might affect the output
+const dateResult = formatter.formatRange(new Date(0), new Date(1));
+assert(formatter.formatRange(new Temporal.Instant(0n), new Temporal.Instant(1000000000n)).startsWith(dateResult),
+       "formatting an Instant should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
index 15762a93c4b..c6cead9e690 100644
--- a/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatRangeToParts/temporal-objects-format-with-era.js
@@ -10,7 +10,7 @@ features: [Temporal]
 locale: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
 
 function checkEra(parts) {
     for (let part of parts) {
@@ -20,10 +20,9 @@ function checkEra(parts) {
     return false;
 }
 
-assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDate(2025, 11, 4), new Temporal.PlainDate(2025, 11, 5))), "formatting a PlainDate should work");
-assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDate(2025, 11, 4), new Temporal.PlainDate(2025, 11, 5))), "formatting a PlainDate should work");
+assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDate(2025, 11, 4 , "gregory"), new Temporal.PlainDate(2025, 11, 5, "gregory"))), "formatting a PlainDate should work");
 assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainYearMonth(2025, 11, "gregory"), new Temporal.PlainYearMonth(2025, 12, "gregory"))), "formatting a PlainYearMonth should work");
 assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainMonthDay(11, 4, "gregory"), new Temporal.PlainMonthDay(11, 14, "gregory"))), "formatting a PlainMonthDay should work");
 assert(!checkEra(formatter.formatRangeToParts(new Temporal.PlainTime(14, 46), new Temporal.PlainTime(17, 46))), "formatting a PlainTime should work");
-assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDateTime(2025, 11, 4, 14, 46), new Temporal.PlainDateTime(2025, 11, 15, 14, 47))), "formatting a PlainDateTime should work");
+assert(checkEra(formatter.formatRangeToParts(new Temporal.PlainDateTime(2025, 11, 4, 14, 16, 0, 0, 0, 0, "gregory"), new Temporal.PlainDateTime(2025, 11, 15, 14, 47, 0, 0, 0, 0, "gregory"))), "formatting a PlainDateTime should work");
 assert(checkEra(formatter.formatRangeToParts(new Temporal.Instant(0n), new Temporal.Instant(1000000000n))), "formatting an Instant should work");
diff --git a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
index 8ae3eb48b13..cec677c1d84 100644
--- a/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
+++ b/test/intl402/DateTimeFormat/prototype/formatToParts/temporal-objects-format-with-era.js
@@ -10,7 +10,7 @@ features: [Temporal]
 locale: [en]
 ---*/
 
-const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow", timeZone: "UTC" });
+const formatter = new Intl.DateTimeFormat(["en"], { era: "narrow" });
 
 function checkEra(parts) {
     for (let part of parts) {