Added mock for code-push plugin in test of demo app. (#1298)

Examples/CodePushDemoApp/__tests__/App.js

@@ -5,6 +5,29 @@ import App from '../App';
 // Note: test renderer must be required after react-native.
 import renderer from 'react-test-renderer';
 
+jest.mock('react-native-code-push', () => {
+  const cp = (_) => (app) => app;
+  Object.assign(cp, {
+    InstallMode: {},
+    CheckFrequency: {},
+    SyncStatus: {},
+    UpdateState: {},
+    DeploymentStatus: {},
+    DEFAULT_UPDATE_DIALOG: {},
+
+    checkForUpdate: jest.fn(),
+    codePushify: jest.fn(),
+    getConfiguration: jest.fn(),
+    getCurrentPackage: jest.fn(),
+    getUpdateMetadata: jest.fn(),
+    log: jest.fn(),
+    notifyAppReady: jest.fn(),
+    notifyApplicationReady: jest.fn(),
+    sync: jest.fn(),
+  });
+  return cp;
+});
+
 it('renders correctly', () => {
   const tree = renderer.create(
     <App />