Fix an analyzer warning in scheduled_test.

pkg/scheduled_test/test/utils.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.
 
 library test_utils;
 
 import 'dart:async';
 
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:scheduled_test/src/utils.dart';
@@ skipping 44 matching lines @@
     // bots, but the Linux and Mac bots have started taking upwards of 5s when
     // running pumpEventQueue, so we're increasing the timeout across the board
     // (see issue 9248).
     currentSchedule.timeout = new Duration(seconds: 10);
   });
 }
 
 /// Creates a metatest with [body] and asserts that it passes.
 ///
 /// This is like [expectTestsPass], but the [test] is set up automatically.
-void expectTestPasses(String description, void body()) =>
+void expectTestPasses(String description, Future body()) =>
   expectTestsPass(description, () => test('test', body));
 
 /// Creates a metatest that runs [testBody], captures its schedule errors, and
 /// passes them to [validator].
 ///
 /// [testBody] is expected to produce an error, while [validator] is expected to
 /// produce none.
-void expectTestFails(String description, void testBody(),
+void expectTestFails(String description, Future testBody(),
     void validator(List<ScheduleError> errors)) {
   expectTestsPass(description, () {
     var errors;
     test('test body', () {
       currentSchedule.onException.schedule(() {
         errors = currentSchedule.errors;
       });
 
       testBody();
     });
 
     test('validate errors', () {
       expect(errors, everyElement(new isInstanceOf<ScheduleError>()));
       validator(errors);
     });
   }, passing: ['validate errors']);
 }