Complete with error if Worker fails.

dart/tests/isolate/spawn_uri_missing_test.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Tests that Isolate.spanUri completes with an error when the given URI
+/// doesn't resolve to an existing resource.
+library test.isolate.spawn_uri_missing_test;
+
+import 'dart:isolate';
+
+import 'dart:async';
+
+import 'package:async_helper/async_helper.dart';
+
+Future doTest() {
+  return Isolate.spawnUri(Uri.base.resolve('no_such_file'), [], null)
+      .then((Isolate isolate) {
+    throw 'Created isolate from missing file';
+  }).catchError((error) {
+    print('An error was thrown as expected');
+    return null;
+  });
+}
+
+main() {
+  asyncTest(doTest);
+}