Simple Express.js app, following REST Architecture, with tests included (Jest + Supertest).

app.js

const express = require('express');
const bodyParser = require('body-parser');

var app = express();
var router = express.Router();

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}));

var tasks = [
        {id: '1', title: "Create REST API with ExpressJS", user:"ivanleonczBR"},
        {id: '2', title: "Build Front-end in AngularJS", user:"erikaUS"},
        {id: '3', title: "Integrate Mobile App with REST API", user:"emiliaDE"},
        {id: '4', title: "Design Tests for Mobile App", user:"charlesUK"}
];

router.get('/tasks', function(req, res) {
    res.send(tasks);
});

router.get('/tasks/:task_id', function(req, res) {
    // tasks start in 0, not 1, for Array context
    res.send(tasks[req.params.task_id - 1]);
});

router.post('/tasks/', function(req, res) {
    // tasks start in 0, not 1, for Array context
    // getting last Array record for generating an id for the new task
    const idx = parseInt(tasks[tasks.length - 1].id) + 1;
    const title = req.body.title;
    const user = req.body.user;
    tasks.push({id: idx.toString(), title:title, user:user});
    res.send("Done!");
});

router.put('/tasks/:task_id', function(req, res) {
    // tasks start in 0, not 1, for Array context
    const idx = req.params.task_id - 1;
    const title = req.body.title;
    const user = req.body.user;
    tasks[idx].title = title;
    tasks[idx].user = user;
    res.send("Done!");
});

router.delete('/tasks/:task_id', function(req, res) {
    // tasks start in 0, not 1, for Array context
    tasks.pop(parseInt(req.params.task_id) -1)
    res.send("Done!");
});

app.use('/api/v1.0', router);

module.exports = app;

app.test.js

const assert = require('assert');
const request = require('supertest');
const app = require('./app')


describe('POST: create new task (id:5)', function() {
    test('It should return response 200.', (done) => {
        request(app).post('/api/v1.0/tasks').send({
            title: "Code Refactor",
            user: "ivanleonczBR"
        }).expect(200).end(function(err, res) {
            done();
        });
    });
});

describe('GET: created task (id:5)', function() {
    test('It respond with json', function() {
        return request(app)
            .get('/api/v1.0/tasks/5')
            .set('Accept', 'application/json')
            .expect('Content-Type', /json/)
            .expect(200)
            .then(response => {
                    assert(response.body.title, 'Code Refactor');
            })
    });
});

describe('PUT: update task (id:5)', function() {
    test('It should return response 200.', function() {
        return request(app)
            .put('/api/v1.0/tasks/5')
            .send({title:'Code Refactor API',user:'ivanleoncz'})
            .expect(200);
    });
});

describe('DELETE: delete task (id:5)', function() {
    test('It should return response 200', function() {
        return request(app)
            .del('/api/v1.0/tasks/5')
            .expect(200);
    });
});

describe('GET: all tasks', function() {
    test('It should response 200.', (done) => {
        request(app).get('/api/v1.0/tasks').then(function(response) {
            expect(200);
            done();
        });
    });
});

package.json

{
  "name": "simple_rest",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "jest --coverage",
    "start": "node server.js"
  },
  "author": "ivanleoncz",
  "license": "GPL-3.0",
  "dependencies": {
    "body-parser": "^1.18.3",
    "ejs": "^2.6.1",
    "express": "^4.16.4"
  },
  "devDependencies": {
    "jest": "^24.5.0",
    "supertest": "^4.0.2"
  }
}

server.js

const app = require('./app');
const port = 3000;

app.listen(port, function() {
    console.log("Server is running: http://localhost:%s", port);
});