Change package scheduled_test to throw TestFailures rather than strings.

pkg/scheduled_test/test/descriptor/file_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:io';
 
 import 'package:path/path.dart' as path;
 import 'package:scheduled_test/descriptor.dart' as d;
 import 'package:scheduled_test/scheduled_test.dart';
 
@@ skipping 82 matching lines @@
       currentSchedule.onException.schedule(() {
         errors = currentSchedule.errors;
       });
 
       d.file('name.txt', 'contents').validate();
     });
 
     test('test 2', () {
       expect(errors, everyElement(new isInstanceOf<ScheduleError>()));
       expect(errors.length, equals(1));
-      expect(errors.first.error,
+      expect(errors.single.error.toString(),
           matches(r"^File not found: '[^']+[\\/]name\.txt'\.$"));
     });
   }, passing: ['test 2']);
 
   expectTestsPass("file().read() returns the contents of the file as a stream",
       () {
     test('test', () {
       expect(byteStreamToString(d.file('name.txt', 'contents').read()),
           completion(equals('contents')));
     });
@@ skipping 44 matching lines @@
 
       schedule(() {
         return new File(path.join(sandbox, 'name.bin'))
             .writeAsBytes([2, 4, 6, 8, 10]);
       });
 
       d.binaryFile('name.bin', [1, 2, 3, 4, 5]).validate();
     });
 
     test('test 2', () {
-      expect(errors, everyElement(new isInstanceOf<ScheduleError>()));
-      expect(errors.map((e) => e.error), equals([
-        "File 'name.bin' didn't contain the expected binary data."
-      ]), verbose: true);
+      expect(errors.single, new isInstanceOf<ScheduleError>());
+      expect(errors.single.error.toString(), equals(
+          "File 'name.bin' didn't contain the expected binary data."));
     });
   }, passing: ['test 2']);
 
   expectTestsPass('matcherFile().create() creates an empty file', () {
     test('test', () {
       scheduleSandbox();
 
       d.matcherFile('name.txt', isNot(isEmpty)).create();
 
       schedule(() {
@@ skipping 78 matching lines @@
 
     test('test 2', () {
       expect(errors, everyElement(new isInstanceOf<ScheduleError>()));
       expect(errors.map((e) => e.error.message), equals([
         "Expected: contains <12>\n"
         "  Actual: [98, 97, 114, 102, 111, 111, 98, 97, 122]\n"
       ]), verbose: true);
     });
   }, passing: ['test 2']);
 }