Testing asynchronous function with mocha

Question

I want to test a asynchronous javascript function that runs in node.js and makes a simple request to a http api:

const HOST = \'localhost\';
const PORT = 80;         


        

Answer 1

I've done a very similar test in my project for an http client. I paste the code here and hope is useful. Here is the client (my nodejs server use express and I use promise for error handling):

var http = require('http');
var querystring = require('querystring');

module.exports = {
  get: function(action, params, res, callback) {
    doPromiseRequest(action, querystring.stringify(params), callback, 'GET', 'application/json')
      .then((response) => callback(response))
      .catch((error) => {
        res.status(500);
        res.render('error', {layout: false, message: error.message, code: 500});
      });
  },
}

function doPromiseRequest(action, params, callback, method, contentType) {
    var options = {
      hostname: 'localhost',
      port: 3000,
      path: '/api/v1/' + action.toString(),
      method: method,
      headers: {
        'Content-Type': contentType,
        'Content-Length': Buffer.byteLength(params)
      }
    };

    return new Promise( (resolve, reject) => {

      var req = http.request(options, 
        function(response) {
          response.setEncoding('utf8');

          var data = '';
          response.on('data', function(chunk) {
            data += chunk;
          });

          response.on('end', function() {
            var parsedResponse;

            try {
              parsedResponse = JSON.parse(data);
            } catch(err) {
              reject({message: `Invalid response from hurricane for ${action}`});
              return;
            }

            if (parsedResponse.error)
              reject(parsedResponse.error);
            else
              resolve(parsedResponse);
          });

          response.on('error', function(err){
            console.log(err.message);
            reject(err);
          });
        });

      req.on('error', function(err) {
        console.log(err);
        reject({message: err.message});
      });

      req.write(params);
      req.end(); 
    });    
}

And here is the test:

var http = require('http');
var expect = require('chai').expect;
var sinon = require('sinon');
var PassThrough = require('stream').PassThrough;

describe('Hurricane Client tests', function() {
  before(function() {
    this.request = sinon.stub(http, 'request');
  });

  after(function() {
    http.request.restore();
  });

  it('should convert get result to object', function(done) {
    var expected = { hello: 'world' };
    var response = new PassThrough();
    response.statusCode = 200;
    response.headers = {}
    response.write(JSON.stringify(expected));
    response.end();

    var request = new PassThrough();

    this.request.callsArgWith(1, response).returns(request);

    client.get('any', {}, null, function(result) {
      expect(result).to.eql(expected);
      done();
    });
  });
});