diff -r 000000000000 -r 6474c204b198 testing/mochitest/tests/browser/browser_fail_add_task.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/testing/mochitest/tests/browser/browser_fail_add_task.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,57 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// This test is designed to fail.
+// It ensures that throwing an asynchronous error from add_task will
+// fail the test.
+
+let passedTests = 0;
+
+function rejectWithTimeout(error = undefined) {
+  let deferred = Promise.defer();
+  executeSoon(function() {
+    ok(true, "we get here after a timeout");
+    deferred.reject(error);
+  });
+  return deferred.promise;
+}
+
+add_task(function failWithoutError() {
+  try {
+    yield rejectWithTimeout();
+  } finally {
+    ++passedTests;
+  }
+});
+
+add_task(function failWithString() {
+  try {
+    yield rejectWithTimeout("Meaningless error");
+  } finally {
+    ++passedTests;
+  }
+});
+
+add_task(function failWithoutInt() {
+  try {
+    yield rejectWithTimeout(42);
+  } finally {
+    ++passedTests;
+  }
+});
+
+
+// This one should display a stack trace
+add_task(function failWithError() {
+  try {
+    yield rejectWithTimeout(new Error("This is an error"));
+  } finally {
+    ++passedTests;
+  }
+});
+
+add_task(function done() {
+  is(passedTests, 4, "Passed all tests");
+});