anchor.diff:        (ServiceEvent event) {
           expect(event.kind, equals('WriteEvent'));
           expect(event.bytesAsString, equals('stderr'));
  -        cancelFutureSubscription(stderrSub).then((_) {
  +        stderrSub.cancel().then((_) {
             completer.complete();
           });
         });
  
positive.code:       (ServiceEvent event) {
          expect(event.kind, equals('WriteEvent'));
          expect(event.bytesAsString, equals('stdout'));
          cancelFutureSubscription(stdoutSub).then((_) {
            completer.complete();
          });
        });
  
negative.code:           expect(event.bytesAsString, equals('print'));
          } else if (eventNumber == 2) {
            expect(event.bytesAsString, equals('\n'));
            stdoutSub.cancel().then((_) {
              completer.complete();
            });
          } else {
  