anchor.diff:        test('should flush periodic timers', () {
           new FakeAsync().run((async) {
             int count = 0;
  -          new Timer.periodic(new Duration(minutes: 30), (Timer timer) {
  +          new Timer.periodic(const Duration(minutes: 30), (Timer timer) {
               if (count == 3) {
                 timer.cancel();
               }
               count++;
             });
  -          async.flushTimers(timeout: new Duration(hours: 20));
  +          async.flushTimers(timeout: const Duration(hours: 20));
             expect(count, 4);
           });
         });
  
positive.code:       test('should run collateral periodic timers', () {
          new FakeAsync().run((async) {
            final log = [];
            new Future.delayed(new Duration(seconds: 2), () {
              log.add('delayed');
            });
            new Timer.periodic(new Duration(seconds: 1), (_) {
              log.add('periodic');
            });
            expect(log, hasLength(0), reason: 'should not flush until asked to');
  
negative.code:       test('it should report the number of pending non periodic timers', () {
          new FakeAsync().run((async) {
            expect(async.nonPeriodicTimerCount, 0);
            Timer timer = new Timer(const Duration(minutes: 30), () {});
            expect(async.nonPeriodicTimerCount, 1);
            new Timer(const Duration(minutes: 20), () {});
            expect(async.nonPeriodicTimerCount, 2);
            async.elapse(const Duration(minutes: 25));
            expect(async.nonPeriodicTimerCount, 1);
            timer.cancel();
            expect(async.nonPeriodicTimerCount, 0);
  