public async Task ObservableItemSourceCollectionItemsSourceChangedReset()
{
tlog.Debug(tag, $"ObservableItemSourceCollectionItemsSourceChanged START");
TaskCompletionSource <bool> tcs = new TaskCompletionSource <bool>(false);
NotifyCollectionChangedEventHandler onChanged = (s, e) => { tcs.TrySetResult(true); };
var para = new TestModel();
var cView = new CollectionView(para);
var testingTarget = new ObservableItemSource(cView.ItemsSource, cView);
testingTarget.CollectionItemsSourceChanged += onChanged;
Assert.IsNotNull(testingTarget, "should be not null");
Assert.IsInstanceOf <ObservableItemSource>(testingTarget, "should be an instance of testing target class!");
para[0] = "test";
para.Clear();
var result = await tcs.Task;
Assert.IsTrue(result, "Change event should be invoked");
Assert.AreEqual(testingTarget.Count, 0, "should be equal.");
tlog.Debug(tag, $"ObservableItemSourceCollectionItemsSourceChanged END (OK)");
}