1 files changed, 112 insertions, 0 deletions
diff --git a/js/src/tests/test262/harness/temporalHelpers-sample-time-zones.js b/js/src/tests/test262/harness/temporalHelpers-sample-time-zones.js
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index 0000000000..43cad8106f
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+++ b/js/src/tests/test262/harness/temporalHelpers-sample-time-zones.js
@@ -0,0 +1,112 @@
+// |reftest| skip-if(!this.hasOwnProperty('Temporal')) -- Temporal is not enabled unconditionally
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+  Verify the time zone arithmetic used in TemporalHelpers.oneShiftTimeZone()
+  against known cases in the implementation's time zone database
+includes: [compareArray.js, temporalHelpers.js]
+features: [Temporal]
+---*/
+
+function checkTimeZoneArithmetic(shiftInstant, testWallTime, testWallDuration, tz, realTimeZoneName) {
+  // No need to test this on hosts that don't provide an Intl object. It's
+  // sufficient that the logic is tested on at least one host.
+  if (typeof globalThis.Intl === "undefined")
+    return;
+
+  const realTz = new Temporal.TimeZone(realTimeZoneName);
+
+  assert.sameValue(
+    tz.getOffsetNanosecondsFor(shiftInstant),
+    realTz.getOffsetNanosecondsFor(shiftInstant),
+    'offset at shift instant'
+  );
+  const minus1 = shiftInstant.subtract({ hours: 1 });
+  assert.sameValue(
+    tz.getOffsetNanosecondsFor(minus1),
+    realTz.getOffsetNanosecondsFor(minus1),
+    'offset at 1 hour before shift'
+  );
+  const plus1 = shiftInstant.add({ hours: 1 });
+  assert.sameValue(
+    tz.getOffsetNanosecondsFor(plus1),
+    realTz.getOffsetNanosecondsFor(plus1),
+    'offset at 1 hour after shift'
+  );
+
+  assert.compareArray(
+    tz.getPossibleInstantsFor(testWallTime).map((i) => i.epochNanoseconds),
+    realTz.getPossibleInstantsFor(testWallTime).map((i) => i.epochNanoseconds),
+    'possible instants for wall time'
+  );
+  const before1 = testWallTime.subtract(testWallDuration);
+  assert.compareArray(
+    tz.getPossibleInstantsFor(before1).map((i) => i.epochNanoseconds),
+    realTz.getPossibleInstantsFor(before1).map((i) => i.epochNanoseconds),
+    'possible instants before wall time'
+  );
+  const after1 = testWallTime.add(testWallDuration);
+  assert.compareArray(
+    tz.getPossibleInstantsFor(after1).map((i) => i.epochNanoseconds),
+    realTz.getPossibleInstantsFor(after1).map((i) => i.epochNanoseconds),
+    'possible instants after wall time'
+  );
+}
+
+// Check a positive DST shift from +00:00 to +01:00
+checkTimeZoneArithmetic(
+  new Temporal.Instant(1616893200000000000n),
+  new Temporal.PlainDateTime(2021, 3, 28, 1),
+  { hours: 1 },
+  TemporalHelpers.oneShiftTimeZone(new Temporal.Instant(1616893200000000000n), 3600e9),
+  'Europe/London',
+);
+
+// Check a negative DST shift from +00:00 to -01:00
+checkTimeZoneArithmetic(
+  new Temporal.Instant(1635642000000000000n),
+  new Temporal.PlainDateTime(2021, 10, 31, 1),
+  { hours: 1 },
+  TemporalHelpers.oneShiftTimeZone(new Temporal.Instant(1635642000000000000n), -3600e9),
+  'Atlantic/Azores',
+);
+
+// Check the no-shift case
+checkTimeZoneArithmetic(
+  new Temporal.Instant(0n),
+  new Temporal.PlainDateTime(1970, 1, 1),
+  { hours: 1 },
+  TemporalHelpers.oneShiftTimeZone(new Temporal.Instant(0n), 0),
+  'UTC',
+);
+
+// Check the cross-date-line sample time zone
+checkTimeZoneArithmetic(
+  Temporal.Instant.from('2011-12-30T10:00:00Z'),
+  Temporal.PlainDateTime.from("2011-12-30T12:00"),
+  { days: 1 },
+  TemporalHelpers.crossDateLineTimeZone(),
+  'Pacific/Apia',
+);
+
+// Check the spring-forward transition of the DST sample time zone
+checkTimeZoneArithmetic(
+  new Temporal.Instant(954669600_000_000_000n),
+  new Temporal.PlainDateTime(2000, 4, 2, 2),
+  { minutes: 30 },
+  TemporalHelpers.springForwardFallBackTimeZone(),
+  'America/Vancouver',
+);
+
+// Check the fall-back transition of the DST sample time zone
+checkTimeZoneArithmetic(
+  new Temporal.Instant(972810000_000_000_000n),
+  new Temporal.PlainDateTime(2000, 10, 29, 2),
+  { minutes: 30 },
+  TemporalHelpers.springForwardFallBackTimeZone(),
+  'America/Vancouver',
+);
+
+reportCompare(0, 0);