chore: sync from fn-registry agent

tests/chart_demo_tests.cpp

@@ -0,0 +1,41 @@
+// E2E tests for chart_demo — Dear ImGui Test Engine.
+// Built only when -DFN_BUILD_TESTS=ON. The same main.cpp from chart_demo is
+// compiled here with FN_TEST_BUILD defined so its int main() is excluded and
+// only render() is reused.
+
+#include "app_base.h"
+#include "imgui.h"
+#include "imgui_te_engine.h"
+#include "imgui_te_context.h"
+
+void render();   // defined in chart_demo/main.cpp
+
+static void register_tests(ImGuiTestEngine* e) {
+    ImGuiTest* t = nullptr;
+
+    // Smoke test: the main window appears and is non-empty.
+    t = IM_REGISTER_TEST(e, "chart_demo", "smoke_window_visible");
+    t->TestFunc = [](ImGuiTestContext* ctx) {
+        ctx->SetRef("fn_registry \xe2\x80\x94 Chart Demo");   // em-dash
+        IM_CHECK(ctx->WindowInfo("").ID != 0);
+    };
+
+    // Cycle through all four tabs. Test engine fails the test if any tab item
+    // is not found or cannot be activated — that is our implicit assertion.
+    t = IM_REGISTER_TEST(e, "chart_demo", "tabs_cycle_all");
+    t->TestFunc = [](ImGuiTestContext* ctx) {
+        ctx->SetRef("fn_registry \xe2\x80\x94 Chart Demo");
+        ctx->ItemClick("##charts/Line Plot");
+        ctx->ItemClick("##charts/Scatter Plot");
+        ctx->ItemClick("##charts/Bar Chart");
+        ctx->ItemClick("##charts/Heatmap");
+    };
+}
+
+int main() {
+    fn::AppConfig cfg{};
+    cfg.title  = "chart_demo_tests";
+    cfg.width  = 1280;
+    cfg.height = 800;
+    return fn::run_app_test(cfg, render, register_tests);
+}