Tweak isolate/spawn_uri_missing*test.dart

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';
 
+const UNEXPECTED_MESSAGE = 'Created isolate from missing file.';
+
 Future doTest() {
   return Isolate.spawnUri(Uri.base.resolve('no_such_file'), [], null)
       .then((Isolate isolate) {
-    throw 'Created isolate from missing file';
+    throw UNEXPECTED_MESSAGE;
   }).catchError((error) {
+    if (error == UNEXPECTED_MESSAGE) throw error;
     print('An error was thrown as expected');
     return null;
   });

[Lasse Reichstein Nielsen, 2014/05/27 12:09:15]

This seem overly complicated. Try this:

  return Isolate.spawnUri(...)
      .then((Isolate isolate) { 
               throw "Created isolate from missing file.";
             }, onError: (e) {
               print("An error was thrown as expected");
             });

[ahe, 2014/05/27 13:31:27]

We talked about this, and I was surprised that it would work.  I think most
people would be surprised, so I prefer keeping the more verbose version.

 }
 
 main() {
   asyncTest(doTest);
 }