diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/collections/Set-constructor-1.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/collections/Set-constructor-1.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,6 @@
+// The Set constructor creates an empty Set by default.
+
+assertEq(Set().size, 0);
+assertEq((new Set).size, 0);
+assertEq(Set(undefined).size, 0);
+assertEq(new Set(undefined).size, 0);