1 files changed, 28 insertions, 0 deletions
diff --git a/js/src/tests/test262/built-ins/Temporal/ZonedDateTime/prototype/toPlainTime/builtin-timezone-no-observable-calls.js b/js/src/tests/test262/built-ins/Temporal/ZonedDateTime/prototype/toPlainTime/builtin-timezone-no-observable-calls.js
new file mode 100644
index 0000000000..e34b4197f7
--- /dev/null
+++ b/js/src/tests/test262/built-ins/Temporal/ZonedDateTime/prototype/toPlainTime/builtin-timezone-no-observable-calls.js
@@ -0,0 +1,28 @@
+// |reftest| skip-if(!this.hasOwnProperty('Temporal')) -- Temporal is not enabled unconditionally
+// 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.zoneddatetime.prototype.toplaintime
+description: >
+  Calling the method on an instance constructed with a builtin time zone causes
+  no observable lookups or calls to time zone methods.
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const getOffsetNanosecondsForOriginal = Object.getOwnPropertyDescriptor(Temporal.TimeZone.prototype, "getOffsetNanosecondsFor");
+Object.defineProperty(Temporal.TimeZone.prototype, "getOffsetNanosecondsFor", {
+  configurable: true,
+  enumerable: false,
+  get() {
+    TemporalHelpers.assertUnreachable("getOffsetNanosecondsFor should not be looked up");
+  },
+});
+
+const instance = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, "UTC", "iso8601");
+instance.toPlainTime();
+
+Object.defineProperty(Temporal.TimeZone.prototype, "getOffsetNanosecondsFor", getOffsetNanosecondsForOriginal);
+
+reportCompare(0, 0);