public void CRUDTests()
        {
            var collection = new JsonPersistingList <TestItem>(key)
            {
                new TestItem("A"),
                new TestItem("B"),
                new TestItem("C"),
            };

            Assert.That(CollectionString, Is.EqualTo("Aa Bb Cc"));

            collection.Add(new TestItem("D"));
            Assert.That(CollectionString, Is.EqualTo("Aa Bb Cc Dd"));

            collection.Insert(2, new TestItem("E"));
            Assert.That(CollectionString, Is.EqualTo("Aa Bb Ee Cc Dd"));

            collection.Remove("C");
            Assert.That(CollectionString, Is.EqualTo("Aa Bb Ee Dd"));

            Assert.Throws(typeof(ArgumentOutOfRangeException), () => collection.Remove("C"));

            collection.Update(new TestItem("E", "q"));
            Assert.That(CollectionString, Is.EqualTo("Aa Bb Eq Dd"));

            collection.Add(new List <TestItem> {
                new TestItem("X"), new TestItem("Y"), new TestItem("Z")
            });
            Assert.That(CollectionString, Is.EqualTo("Aa Bb Eq Dd Xx Yy Zz"));

            collection.Add(new TestItem("x"), new TestItem("y"), new TestItem("z"));
            Assert.That(CollectionString, Is.EqualTo("Aa Bb Eq Dd Xx Yy Zz xx yy zz"));

            Assert.Throws(typeof(ApplicationException), () => collection.Add(new TestItem("X", "1"), new TestItem("W", "2")));

            collection.Clear();
            Assert.That(CollectionString, Is.EqualTo(""));
        }
 protected override void InsertItem(int index, T item)
 {
     persistence.Insert(index, item);
     base.InsertItem(index, item);
 }