public void replacing_an_item_updates_the_mean()
{
var model = new PostedTimeCollectionModel();
var observer = model.CreateObserver();
model.Add(PT(1, PostedTimeType.Normal, 1));
model.ReplaceCurrent(PT(10, PostedTimeType.Normal, 1));
Assert.Equal(TS(10), model.Mean);
Assert.True(observer.HasChanged(x => x.Mean));
}