Extract XCUI selection model and layout lab click selection

tests/Core/UI/CMakeLists.txt

@@ -6,6 +6,7 @@ set(UI_TEST_SOURCES
     test_ui_core.cpp
     test_ui_editor_collection_primitives.cpp
     test_layout_engine.cpp
+    test_ui_selection_model.cpp
     test_ui_runtime.cpp
     test_ui_text_editing.cpp
     test_ui_text_input_controller.cpp

tests/Core/UI/test_ui_selection_model.cpp

@@ -0,0 +1,42 @@
+#include <gtest/gtest.h>
+
+#include <XCEngine/UI/Widgets/UISelectionModel.h>
+
+namespace {
+
+using XCEngine::UI::Widgets::UISelectionModel;
+
+TEST(UISelectionModelTest, SetAndClearSelectionTrackCurrentId) {
+    UISelectionModel selection = {};
+
+    EXPECT_FALSE(selection.HasSelection());
+    EXPECT_TRUE(selection.GetSelectedId().empty());
+
+    EXPECT_TRUE(selection.SetSelection("assetLighting"));
+    EXPECT_TRUE(selection.HasSelection());
+    EXPECT_TRUE(selection.IsSelected("assetLighting"));
+    EXPECT_EQ(selection.GetSelectedId(), "assetLighting");
+
+    EXPECT_FALSE(selection.SetSelection("assetLighting"));
+    EXPECT_TRUE(selection.ClearSelection());
+    EXPECT_FALSE(selection.HasSelection());
+    EXPECT_TRUE(selection.GetSelectedId().empty());
+    EXPECT_FALSE(selection.ClearSelection());
+}
+
+TEST(UISelectionModelTest, ToggleSelectionSelectsAndDeselectsMatchingId) {
+    UISelectionModel selection = {};
+
+    EXPECT_TRUE(selection.ToggleSelection("treeScenes"));
+    EXPECT_EQ(selection.GetSelectedId(), "treeScenes");
+
+    EXPECT_TRUE(selection.ToggleSelection("treeScenes"));
+    EXPECT_TRUE(selection.GetSelectedId().empty());
+
+    EXPECT_TRUE(selection.ToggleSelection("treeMaterials"));
+    EXPECT_EQ(selection.GetSelectedId(), "treeMaterials");
+    EXPECT_TRUE(selection.ToggleSelection("treeUi"));
+    EXPECT_EQ(selection.GetSelectedId(), "treeUi");
+}
+
+} // namespace