Temporal.ZonedDateTime.p.with() with broken offset property on receiver

Tests for the normative change made to Temporal in
https://github.com/tc39/proposal-temporal/pull/1865

test/built-ins/Temporal/ZonedDateTime/prototype/with/receiver-offset-broken.js

@@ -0,0 +1,76 @@
+// 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.zoneddatetime.protoype.with
+description: TypeError thrown when the offset field of the receiver is broken
+info: |
+    10. Let _fieldNames_ be ? CalendarFields(_calendar_, « *"day"*, *"hour"*, *"microsecond"*, *"millisecond"*, *"minute"*, *"month"*, *"monthCode"*, *"nanosecond"*, *"second"*, *"year"* »).
+    11. Append *"offset"* to _fieldNames_.
+    12. Let _partialZonedDateTime_ be ? PreparePartialTemporalFields(_temporalZonedDateTimeLike_, _fieldNames_).
+    ...
+    17. Append *"timeZone"* to _fieldNames_.
+    18. Let _fields_ be ? PrepareTemporalFields(_zonedDateTime_, _fieldNames_, « *"timeZone"*, *"offset"* »).
+    19. Set _fields_ to ? CalendarMergeFields(_calendar_, _fields_, _partialZonedDateTime_).
+    20. Set _fields_ to ? PrepareTemporalFields(_fields_, _fieldNames_, « *"timeZone"*, *"offset"* »).
+    21. Let _offsetString_ be ! Get(_fields_, *"offset"*).
+    22. Assert: Type(_offsetString_) is String.
+features: [Temporal]
+---*/
+
+class ObservedCalendar extends Temporal.Calendar {
+  constructor() {
+    super("iso8601");
+    this.resetCalls();
+  }
+
+  toString() {
+    return "observed-calendar";
+  }
+
+  mergeFields(original, additional) {
+    this.mergeFieldsCalled++;
+    const result = super.mergeFields(original, additional);
+    result.offset = Symbol("can't convert to string");
+    return result;
+  }
+
+  resetCalls() {
+    this.mergeFieldsCalled = 0;
+  }
+}
+
+const calendar = new ObservedCalendar();
+const dateTime = new Temporal.ZonedDateTime(1_000_000_000_000_000_000n, "UTC", calendar);
+
+// Test throw in step 12
+
+assert.throws(TypeError, () => dateTime.with({ offset: Symbol("can't convert to string") }), "conversion failure on ZonedDateTime-like");
+assert.sameValue(calendar.mergeFieldsCalled, 0, "calendar.mergeFields should not be called");
+
+calendar.resetCalls();
+
+// Test throw in step 20 (before sabotaging the ZonedDateTime instance)
+
+assert.throws(TypeError, () => dateTime.with({ year: 2002 }), "conversion failure on sabotaged return value from mergeFields");
+assert.sameValue(calendar.mergeFieldsCalled, 1, "calendar.mergeFields was called once");
+
+calendar.resetCalls();
+
+// Test throw in step 18
+
+Object.defineProperty(dateTime, "offset", { value: Symbol("can't convert to string"), configurable: true });
+
+assert.throws(TypeError, () => dateTime.with({ year: 2002 }), "conversion failure on sabotaged offset field of receiver");
+assert.sameValue(calendar.mergeFieldsCalled, 0, "calendar.mergeFields should not be called");
+
+calendar.resetCalls();
+
+// Test offset being required in step 18
+
+Object.defineProperty(dateTime, "offset", { value: undefined });
+
+assert.throws(TypeError, () => dateTime.with({ year: 2002 }), "offset property is required on receiver");
+assert.sameValue(calendar.mergeFieldsCalled, 0, "calendar.mergeFields should not be called");
+
+calendar.resetCalls();