1 files changed, 24 insertions, 0 deletions
diff --git a/js/src/tests/test262/built-ins/Temporal/ZonedDateTime/prototype/add/negative-epochnanoseconds.js b/js/src/tests/test262/built-ins/Temporal/ZonedDateTime/prototype/add/negative-epochnanoseconds.js
new file mode 100644
index 0000000000..b52a6329bd
--- /dev/null
+++ b/js/src/tests/test262/built-ins/Temporal/ZonedDateTime/prototype/add/negative-epochnanoseconds.js
@@ -0,0 +1,24 @@
+// |reftest| skip-if(!this.hasOwnProperty('Temporal')) -- Temporal is not enabled unconditionally
+// 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.prototype.add
+description: A pre-epoch value is handled correctly by the modulo operation in GetISOPartsFromEpoch
+info: |
+    sec-temporal-getisopartsfromepoch step 1:
+      1. Let _remainderNs_ be the mathematical value whose sign is the sign of _epochNanoseconds_ and whose magnitude is abs(_epochNanoseconds_) modulo 10<sup>6</sup>.
+    sec-temporal-builtintimezonegetplaindatetimefor step 2:
+      2. Let _result_ be ! GetISOPartsFromEpoch(_instant_.[[Nanoseconds]]).
+features: [Temporal]
+---*/
+
+const datetime = new Temporal.ZonedDateTime(-13849764_999_999_999n, "UTC");
+
+// This code path shows up anywhere we convert an exact time, before the Unix
+// epoch, with nonzero microseconds or nanoseconds, into a wall time.
+
+const result = datetime.add(new Temporal.Duration(0, 0, 0, 1));
+assert.sameValue(result.epochNanoseconds, -13763364_999_999_999n);
+
+reportCompare(0, 0);