[tests] make the function expression an iife to run the test

test/mjsunit/es6/promises.js

Index: test/mjsunit/es6/promises.js
diff --git a/test/mjsunit/es6/promises.js b/test/mjsunit/es6/promises.js
index 0af7a882e7f30c0415b3c0e98090a4666ba00969..7813b11929e5e4936c863c601ae3759a532c026a 100644
--- a/test/mjsunit/es6/promises.js
+++ b/test/mjsunit/es6/promises.js
@@ -982,7 +982,7 @@ function assertAsyncDone(iteration) {
   var promise = new Promise(function(res) { resolve = res; });
   resolve({ then() { thenCalled = true; throw new Error(); } });
   assertLater(function() { return thenCalled; }, "resolve-with-thenable");
-});
+})();
 
 (function() {
   var calledWith;