public void Test_ConcurrentObservableCollection_RemoveRange_ByItems_IEnumerable() { var initial = Enumerable.Range(0, 100).Select(x => new KeyValuePair <int, int>(x, x)); var toRemove = Enumerable.Range(1, 40).Select(x => x * 2); var collection = new ConcurrentObservableDictionary <int, int>(); collection.AddRange(initial); Assert.AreEqual(100, collection.Count); // Record all the collection changed events List <(object, NotifyCollectionChangedEventArgs)> returnedList = new List <(object, NotifyCollectionChangedEventArgs)>(); collection.CollectionChanged += (s, e) => returnedList.Add((s, e)); collection.RemoveRange(toRemove); // Check just one collection changed event was fired Assert.AreEqual(1, returnedList.Count); (var returnedObject, var returnedArgs) = returnedList[0]; Assert.IsNotNull(returnedObject); Assert.IsNotNull(returnedArgs); Assert.AreEqual(returnedObject, collection); Assert.AreEqual(NotifyCollectionChangedAction.Remove, returnedArgs.Action); Assert.AreEqual(-1, returnedArgs.OldStartingIndex); Assert.IsNull(returnedArgs.NewItems); Assert.IsNotNull(returnedArgs.OldItems); Assert.AreEqual(toRemove.Count(), returnedArgs.OldItems.Count); Assert.IsTrue(CollectionsAreEqual(toRemove, returnedArgs.OldItems)); }