Temporal: Add coverage for rounding/totaling zero duration (tc39#4774)

Author: catamorphism

test/built-ins/Temporal/Duration/prototype/round/zero-duration.js

@@ -0,0 +1,42 @@
+// 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.duration.prototype.round
+description: Rounding zero duration returns 0
+includes: [temporalHelpers.js]
+features: [Temporal]
+---*/
+
+const zero = new Temporal.Duration();
+
+let relativeToDates = [
+  new Temporal.ZonedDateTime(0n, 'UTC'),
+  new Temporal.PlainDateTime(1970, 1, 1)
+];
+
+let units = [
+  { smallestUnit: 'hours', largestUnit: 'days' },
+  { smallestUnit: 'minutes', largestUnit: 'days' },
+  { smallestUnit: 'seconds', largestUnit: 'days' },
+  { smallestUnit: 'hours', largestUnit: 'weeks' },
+  { smallestUnit: 'minutes', largestUnit: 'weeks' },
+  { smallestUnit: 'seconds', largestUnit: 'weeks' },
+  { smallestUnit: 'hours', largestUnit: 'months' },
+  { smallestUnit: 'minutes', largestUnit: 'months' },
+  { smallestUnit: 'seconds', largestUnit: 'months' },
+  { smallestUnit: 'hours', largestUnit: 'years' },
+  { smallestUnit: 'minutes', largestUnit: 'years' },
+  { smallestUnit: 'seconds', largestUnit: 'years' }
+];
+
+for (const relativeTo of relativeToDates) {
+  for (const unit of units) {
+    TemporalHelpers.assertDuration(zero.round({
+      smallestUnit: unit.smallestUnit,
+      largestUnit: unit.largestUnit,
+      relativeTo
+    }),
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
+  }
+}

test/built-ins/Temporal/Duration/prototype/total/zero-duration.js

@@ -0,0 +1,23 @@
+// 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.duration.prototype.total
+description: Totaling zero duration returns 0
+features: [Temporal]
+---*/
+
+const zero = new Temporal.Duration();
+
+let relativeToDates = [
+  new Temporal.ZonedDateTime(0n, 'UTC'),
+  new Temporal.PlainDateTime(1970, 1, 1)
+];
+
+let units = [ 'days', 'weeks', 'months', 'years' ];
+
+for (const relativeTo of relativeToDates) {
+  for (const unit of units) {
+    assert.sameValue(zero.total({ unit, relativeTo }), 0);
+  }
+}