private Test CreateAddItemsTest() { return(new TestCase("AddItems", () => { AssertDistinctIntancesNotEmpty(); var collection = GetSafeDefaultInstance(); var handler = new CollectionHandler <TCollection, TItem>(collection, Context); var initialContent = new ReadOnlyCollection <TItem>(new List <TItem>(collection)); foreach (var item in DistinctInstances) { if (!initialContent.Contains(item)) { handler.AddSingleItemOk(item); } if (AcceptEqualItems) { handler.AddDuplicateItemOk(item); } else { handler.AddDuplicateItemFails(item); } } })); }