public void ReactsAndNotifiesOnSourceChanges()
{
var source = new ObservableCollection <double>(new[] { 1.0, 2, 3 });
var tracker = new DoubleAverageTracker(source, source.ObserveCollectionChangedSlim(false), -1);
Assert.AreEqual(source.Average(), tracker.Value);
int count = 0;
tracker.ObservePropertyChanged(x => x.Value, false)
.Subscribe(_ => count++);
source.Remove(2);
Assert.AreEqual(0, count);
Assert.AreEqual(source.Average(), tracker.Value);
source.Remove(1);
Assert.AreEqual(1, count);
Assert.AreEqual(source.Average(), tracker.Value);
source.Remove(3);
Assert.AreEqual(2, count);
Assert.AreEqual(-1, tracker.Value);
source.Add(2);
Assert.AreEqual(3, count);
Assert.AreEqual(source.Average(), tracker.Value);
}
