diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/arrow-functions/params-2.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/arrow-functions/params-2.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,6 @@
+// (a) => expr
+
+var f = (a) => 2 * a;  // parens are allowed
+assertEq(f(12), 24);
+var g = (a, b) => a + b;
+assertEq([1, 2, 3, 4, 5].reduce((a, b) => a + b), 15);