keep node_env if provided from upstream

Created by: DianaSuvorova

Hello, this is tiny configuration that would allow the use of react-script start for browser e2e tests.

  "scripts": {
    "start": "react-scripts start",
    "start:test": "NODE_ENV=test react-scripts start",
...

So then inside index.js I could decide wether it is a dev build or integration test build.

if (process.env.NODE_ENV === 'test') {
  Enzyme.configure({ adapter: new Adapter() });

  const wrap = (<Provider store={store}><App />< /Provider>);

  const el = Enzyme.mount(wrap,
    { attachTo: document.getElementById('root') }
  );
  iTest(el);
} else {
  ReactDOM.render(
    <Provider store={store}>
      <App />
    </Provider>,
    document.getElementById('root')
  );
}

More details here: https://github.com/DianaSuvorova/Demo-project/blob/master/frontend/package.json https://github.com/DianaSuvorova/Demo-project/blob/master/frontend/src/index.js

Thanks, Diana