How to export node express app for chai-http

After receiving some good feedback, I found this solution works best for me, based on Gomzy's answer and Vikash Singh's answer.

In server.js I'm connecting to the mongo pool, then emitting the 'ready' event on the express app. Then in the test, I can use before() to wait for 'ready' event to be emitted on the app. Once that happens, I'm good to start executing the test.

server.js

import express from 'express';
import bodyParser from 'body-parser';
import MongoPool from './lib/MongoPool';
let app = express();
let port = process.env.PORT || 5000;
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());

(async () => {
    await MongoPool.connect();
    console.log("Connected to db.");
    require('./api').default(app);
    app.listen(port, () => {
        console.log(`Listening on port ${port}.`)
        app.emit("ready");
    });
})();

export default app;

test.js

//Require the dev-dependencies
import chai from 'chai';
import chaiHttp from 'chai-http';
import server from '../src/server'; 
let should = chai.should();
chai.use(chaiHttp);

before(done => {
  server.on("ready", () => {
    done();
  })
})
describe('Forecast', () => {
  describe('/GET forecast', () => {
    it('it should GET the forecast', (done) => {
      chai.request(server)
          .get('/api/forecast?type=grid&lat=39.2667&long=-81.5615')
          .end((err, res) => {
              res.should.have.status(200);
            done();
          });
    });
  });

});

Express app is an instance of EventEmitter so we can easily subscribe to events. i.e app can listen for the 'ready' event.

Your server.js file will look like below,

import express from 'express';
import api from './api';
import MongoPool from './lib/MongoPool';
let app = express();
let port = process.env.PORT || 3000;

app.on('ready', function() {
  app.listen(3000, function() {
    console.log('app is ready');
  });
});

MongoPool.connect((err, success) => {
  if (err) throw err;
  if (success) {
    console.log('Connected to db.');
    // apply express router endpoints to app
    api(app);

    // All OK - fire (emit) a ready event.
    app.emit('ready');
  } else {
    throw 'Couldnt connect to db';
  }
});

export default app;