public void LastSelectionChangeWasObserved()
        {
            //Arrange
            ClassUnderTest.SelectedItem = ClassUnderTest.Items.FirstOrDefault();

            SelectionChangedEventArgs <TestViewModel> selectionChangedEventArgs = null;
            var subscription = ClassUnderTest.SelectionChanged.Subscribe(ea => selectionChangedEventArgs = ea);

            //Act
            ClassUnderTest.SelectedItem = ClassUnderTest.Items.FirstOrDefault();

            //Assert
            selectionChangedEventArgs.Should().NotBeNull();

            subscription.Dispose();
        }
        public void SelectionChanged_NotificationIsPublished()
        {
            //Arrange
            SelectionChangedEventArgs <TestViewModel> selectionChangedEventArgs = null;
            var subscription = ClassUnderTest.SelectionChanged.Subscribe(ea => selectionChangedEventArgs = ea);

            //Act
            ClassUnderTest.SelectedItem = ClassUnderTest.Items.FirstOrDefault();

            //Assert
            selectionChangedEventArgs.Should().NotBeNull();
            selectionChangedEventArgs.OldValue.Should().BeNull();
            selectionChangedEventArgs.NewValue.Should().Be(ClassUnderTest.SelectedItem);

            subscription.Dispose();
        }