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