diff -r 000000000000 -r 6474c204b198 js/src/jit-test/lib/asserts.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/lib/asserts.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,67 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+
+load(libdir + "../../tests/ecma_6/shell.js");
+
+if (typeof assertWarning === 'undefined') {
+    var assertWarning = function assertWarning(f, errorClass, msg) {
+        var hadWerror = options().split(",").indexOf("werror") !== -1;
+
+        // Ensure the "werror" option is disabled.
+        if (hadWerror)
+            options("werror");
+
+        try {
+            f();
+        } catch (exc) {
+            if (hadWerror)
+                options("werror");
+
+            // print() rather than throw a different exception value, in case
+            // the caller wants exc.stack.
+            if (msg)
+                print("assertWarning: " + msg);
+            print("assertWarning: Unexpected exception calling " + f +
+                  " with warnings-as-errors disabled");
+            throw exc;
+        }
+
+        // Enable the "werror" option.
+        options("werror");
+
+        try {
+            assertThrowsInstanceOf(f, errorClass, msg);
+        } catch (exc) {
+            if (msg)
+                print("assertWarning: " + msg);
+            throw exc;
+        } finally {
+            if (!hadWerror)
+                options("werror");
+        }
+    };
+}
+
+if (typeof assertNoWarning === 'undefined') {
+    var assertNoWarning = function assertWarning(f, msg) {
+        // Ensure the "werror" option is enabled.
+        var hadWerror = options().split(",").indexOf("werror") !== -1;
+        if (!hadWerror)
+            options("werror");
+
+        try {
+            f();
+        } catch (exc) {
+            if (msg)
+                print("assertNoWarning: " + msg);
+            print("assertNoWarning: Unexpected exception calling " + f +
+                  "with warnings-as-errors enabled");
+            throw exc;
+        } finally {
+            if (!hadWerror)
+                options("werror");
+        }
+    };
+}