server.js

const readFileAsync = file => new Promise((resolve, reject) => {
  fs.readFile(file, (err, data) => err ? reject(err) : resolve(data));
});

const records = async (req, res) => {
  await readFileAsync('phonebook.txt');
  const count = readBook.toString().split('\n').length - 1;
  const str = `Welcome to The Phonebook\nRecords count: ${count}`; 
  res.write(str);
};

export default (port, callback) => {
  const server = http.createServer((req, res) => {
    await records(req, res);
    res.end(callback);
  });
  server.listen(port, () => {
    console.log('Server has been started');
  });
};


TEST!!!!
    
import httpAdapter from 'axios/lib/adapters/http';
import server from './solution';

axios.defaults.adapter = httpAdapter;

const hostname = 'localhost';
const port = 9000;
const url = `http://${hostname}:${port}`;

describe('Phonebook', () => {
  it('GET /', (done) => {
    server(port, async () => {
      try {
        const res = await axios.get(url);
        expect(res.data).toBe('Welcome to The Phonebook\nRecords count: 1000');
        done();
      } catch (e) {
        done.fail(e);
      }
    });
  });
});