test: refactor test:demo script into demo/*/test.sh

demo/reactjs/src/index.tsx

@@ -0,0 +1,20 @@
+import { createRoot } from 'react-dom/client';
+import {
+  BrowserRouter as Router,
+  Routes,
+  Route,
+} from "react-router-dom";
+import './index.css';
+import { App } from './App';
+import { App as AppWithHooks } from './AppWithHooks';
+
+const container = document.getElementById('root');
+const root = createRoot(container!);
+root.render(
+  <Router>
+    <Routes>
+      <Route path="/" Component={App}/>
+      <Route path="/with-hooks" Component={AppWithHooks}/>
+    </Routes>
+  </Router>
+);