Change package scheduled_test to throw TestFailures rather than strings.

pkg/scheduled_test/test/descriptor/async_test.dart

Index: pkg/scheduled_test/test/descriptor/async_test.dart
diff --git a/pkg/scheduled_test/test/descriptor/async_test.dart b/pkg/scheduled_test/test/descriptor/async_test.dart
index b4fde985b93c34be5d57d71f44aad2f13700a903..15763bb54edd53031cc4c7b3603d5879a146359e 100644
--- a/pkg/scheduled_test/test/descriptor/async_test.dart
+++ b/pkg/scheduled_test/test/descriptor/async_test.dart
@@ -70,10 +70,9 @@ void main() {
     });
 
     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']);
 
@@ -113,9 +112,8 @@ void main() {
     });
 
     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']);