public void Filter () { ItemCollection c = new ItemsControl ().Items; c.Add (1); c.Add (-1); Assert.AreEqual (c.Count, 2, "1"); c.Filter = FilterFilter; Assert.AreEqual (c.Count, 1, "2"); c.Filter = null; Assert.AreEqual (c.Count, 2, "3"); c.Filter = FilterFilter; c.Add (2); Assert.AreEqual (c.Count, 2, "4"); c.Filter = null; Assert.AreEqual (c.Count, 3, "5"); c.Filter = FilterFilter; c.Remove (-1); c.Filter = null; Assert.AreEqual (c.Count, 2, "6"); }