anchor.diff:          var todos = [];
           var eventsCount = 0;
           var subscription = childRef.onChildAdded.listen(expectAsync((event) {
  -          var snapshot = event.snapshot;
  -          todos.add(snapshot.val());
  +          var val = event.snapshot.val();
  +          todos.add(val);
             eventsCount++;
             expect(eventsCount, isNonZero);
             expect(eventsCount, lessThan(4));
  -          expect(snapshot.val(),
  +          expect(val,
                 anyOf("Programming", "Cooking", "Walking with dog"));
           }, count: 3));
   
  
positive.code:         childRef.push("Walking with dog");
  
          var subscription = childRef.onChildRemoved.listen(expectAsync((event) {
            var snapshot = event.snapshot;
            expect(snapshot.val(), "Programming");
            expect(snapshot.val(), isNot("Cooking"));
          }, count: 1));
  
          childRef.child(childKey).remove();
  
negative.code:         childRef.set(["Programming", "Cooking", "Walking with dog"]);
  
          var subscription = childRef.onValue.listen(expectAsync((event) {
            var todos = event.snapshot.val();
            expect(todos, isNotNull);
            expect(todos.length, 3);
  