After assignment return right hand side value instead of undefined

test/mjsunit/object-prevent-extensions.js

Index: test/mjsunit/object-prevent-extensions.js
diff --git a/test/mjsunit/object-prevent-extensions.js b/test/mjsunit/object-prevent-extensions.js
index 322a2cb5431655943a0c5a8878a8b293fc4cf4bd..6b9184d88bdd89aadf8ced092b514db9f1396399 100644
--- a/test/mjsunit/object-prevent-extensions.js
+++ b/test/mjsunit/object-prevent-extensions.js
@@ -114,3 +114,15 @@ Object.preventExtensions(foo);
 
 foo.x = 29;
 assertEquals(undefined, foo.x);
+
+// when Object.isExtensible(o) === false
+// assignment should return right hand side value
+var o = Object.preventExtensions({});
+var v = o.v = 50;
+assertEquals(undefined, o.v);
+assertEquals(50, v);
+
+// test same behavior as above, but for integer properties
+var n = o[0] = 100;
+assertEquals(undefined, o[0]);
+assertEquals(100, n);