Change package scheduled_test to throw TestFailures rather than strings.

pkg/scheduled_test/test/descriptor/async_test.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 
 import 'package:scheduled_test/descriptor.dart' as d;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../metatest.dart';
@@ skipping 52 matching lines @@
       currentSchedule.onException.schedule(() {
         errors = currentSchedule.errors;
       });
 
       d.async(pumpEventQueue().then((_) {
         return d.file('name.txt', 'contents');
       })).validate();
     });
 
     test('test 2', () {
-      expect(errors, everyElement(new isInstanceOf<ScheduleError>()));
-      expect(errors.length, equals(1));
-      expect(errors.first.error,
-          matches(r"^File not found: '[^']+[\\/]name\.txt'\.$"));
+      expect(errors.single, new isInstanceOf<ScheduleError>());
+      expect(errors.single.error.toString(),
+             matches(r"^File not found: '[^']+[\\/]name\.txt'\.$"));
     });
   }, passing: ['test 2']);
 
   expectTestsPass("async().validate() forwards to directory().validate", () {
     test('test', () {
       scheduleSandbox();
 
       d.dir('dir', [
         d.file('file1.txt', 'contents1'),
         d.file('file2.txt', 'contents2')
@@ skipping 19 matching lines @@
 
       d.async(pumpEventQueue().then((_) {
         return d.dir('dir', [
           d.file('file1.txt', 'contents1'),
           d.file('file2.txt', 'contents2')
         ]);
       })).validate();
     });
 
     test('test 2', () {
-      expect(errors, everyElement(new isInstanceOf<ScheduleError>()));
-      expect(errors.length, equals(1));
-      expect(errors.first.error,
+      expect(errors.single, new isInstanceOf<ScheduleError>());
+      expect(errors.single.error.toString(),
           matches(r"^Directory not found: '[^']+[\\/]dir'\.$"));
     });
   }, passing: ['test 2']);
 }