Add basic react-navigator usage

__tests__/App-test.tsx

@@ -4,11 +4,13 @@
 
 import 'react-native';
 import React from 'react';
-import App from '../App';
+import App from '../src/App';
 
 // Note: test renderer must be required after react-native.
 import renderer from 'react-test-renderer';
 
 it('renders correctly', () => {
-  renderer.create(<App />);
+  renderer.act(() => {
+    renderer.create(<App />);
+  });
 });