anchor.diff:          childRef.push("Walking with dog");
   
           var subscription = childRef.onChildChanged.listen(expectAsync((event) {
  -          var snapshot = event.snapshot;
  -          expect(snapshot.val(), "Programming a Firebase lib");
  -          expect(snapshot.val(), isNot("Programming"));
  -          expect(snapshot.val(), isNot("Cooking"));
  +          var val = event.snapshot.val();
  +          expect(val, "Programming a Firebase lib");
  +          expect(val, isNot("Programming"));
  +          expect(val, isNot("Cooking"));
           }, count: 1));
   
           childRef.child(childKey).set("Programming a Firebase lib");
  
positive.code:         childRef.set(["Programming", "Cooking", "Walking with dog"]);
  
          var subscription = childRef.onValue.listen(expectAsync((event) {
            var snapshot = event.snapshot;
            var todos = event.snapshot.val();
            expect(todos, isNotNull);
            expect(todos.length, 3);
  
negative.code: 
          var subscription =
              childRef.orderByPriority().onChildMoved.listen(expectAsync((event) {
                    var val = event.snapshot.val();
                    expect(val, "Programming");
                    expect(val, isNot("Cooking"));
                  }, count: 1));
  
          childPushRef.setPriority(100);
  