public void CollapseAllTest()
        {
            var element = CreateCustomNode("AMember", "CategoryA.SubCategoryA.ClassA");

            model.Add(element);

            element = CreateCustomNode("BMember", "CategoryB.SubCategoryB.ClassB");
            model.Add(element);

            viewModel.BrowserRootCategories[1].IsExpanded = true;
            viewModel.BrowserRootCategories[1].SubCategories[0].IsExpanded = true;

            viewModel.CollapseAll(viewModel.BrowserRootCategories);

            Assert.IsFalse(viewModel.BrowserRootCategories[1].IsExpanded);
            Assert.IsFalse(viewModel.BrowserRootCategories[1].SubCategories[0].IsExpanded);
        }