public void UpdateBasedOnElements()
{
var a = new TestElement("0", "A");
var c = new ObservableCollectionEx <TestElement> {
a,
new TestElement("1", "C")
};
var source = new[] { new TestElement("2", "B"), new TestElement("0", "A") };
c.Update(source, te => te.Id);
Assert.That(c.Count, Is.EqualTo(2));
Assert.That(c[0], Is.SameAs(source[0]));
Assert.That(c[1], Is.SameAs(a));
}