public void adding_an_item_updates_the_mean()
{
var model = new DoubleCollectionModel();
var observer = model.CreateObserver();
model.Add(1d);
Assert.Equal(1d, model.Mean);
model.Add(1d);
Assert.Equal(1d, model.Mean);
model.Add(4d);
Assert.Equal(2d, model.Mean);
Assert.Equal(2, observer.GetChangeCount(x => x.Mean));
}