diff -r 000000000000 -r 6474c204b198 js/src/jsapi-tests/testSameValue.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jsapi-tests/testSameValue.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,27 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jsapi-tests/tests.h"
+
+BEGIN_TEST(testSameValue)
+{
+
+    /*
+     * NB: passing a double that fits in an integer jsval is API misuse.  As a
+     * matter of defense in depth, however, JS_SameValue should return the
+     * correct result comparing a positive-zero double to a negative-zero
+     * double, and this is believed to be the only way to make such a
+     * comparison possible.
+     */
+    jsval v1 = DOUBLE_TO_JSVAL(0.0);
+    jsval v2 = DOUBLE_TO_JSVAL(-0.0);
+    bool same;
+    CHECK(JS_SameValue(cx, v1, v2, &same));
+    CHECK(!same);
+    return true;
+}
+END_TEST(testSameValue)