pokemon.trade/app/javascript/packs/frontend/app.jsx

import React from 'react';
import {BrowserRouter, Route} from 'react-router-dom';
import {hot} from 'react-hot-loader/root';

import TestComponent from './components/test_component';

class App extends React.Component {
  render() {
    return (
      <BrowserRouter>
        <Route exact path="/" component={TestComponent} />
      </BrowserRouter>
    );
  }
}

export default hot(App);