anchor.diff:  
           var todos = [];
           var eventsCount = 0;
  -        var subscription = childRef.onChildAdded.listen(expectAsync((event) {
  +        var subscription = childRef.onChildAdded.listen(expectAsync1((event) {
             var val = event.snapshot.val();
             todos.add(val);
             eventsCount++;
  
positive.code:         childRef.push("Cooking");
          childRef.push("Walking with dog");
  
          var subscription = childRef.onChildChanged.listen(expectAsync((event) {
            var val = event.snapshot.val();
            expect(val, "Programming a Firebase lib");
            expect(val, isNot("Programming"));
  
negative.code:         var childRef = ref.child("todos");
          childRef.set(["Programming", "Cooking", "Walking with dog"]);
  
          var subscription = childRef.onValue.listen(expectAsync1((event) {
            var todos = event.snapshot.val();
            expect(todos, isNotNull);
            expect(todos.length, 3);
  