✅ test(App): add unit tests

src/App.test.tsx

@@ -0,0 +1,13 @@
+import { render, screen } from '@testing-library/react'
+
+import App from './App'
+
+describe('App component', () => {
+  test('renders MainPage without crashing', async () => {
+    render(<App />)
+
+    expect(screen.getByLabelText('loading-screen')).toBeInTheDocument()
+    expect(await screen.findByText('Robotics Engineer')).toBeInTheDocument()
+    expect(screen.queryByLabelText('loading-screen')).not.toBeInTheDocument()
+  })
+})