anchor.diff:                  .snapshots
                   .listen((QuerySnapshot querySnapshot) {});
           subscription.cancel();
  -        await new Future<Null>.delayed(Duration.ZERO);
  +        await new Future<Null>.delayed(Duration.zero);
           expect(
             log,
             equals(<Matcher>[
  
positive.code:                 .snapshots
                  .listen((QuerySnapshot querySnapshot) {});
          subscription.cancel();
          await new Future<Null>.delayed(Duration.ZERO);
          expect(
            log,
            equals(<Matcher>[
  
negative.code:         expect(snapshot.reference.path, equals('path/to/foo'));
          expect(snapshot.data, equals(kMockDocumentSnapshotData));
          // Flush the async removeListener call
          await new Future<Null>.delayed(Duration.zero);
          expect(
            log,
            <Matcher>[
  