Mocking email function in nodejs

Question

I've got a mailer function I've built and trying to shore up the coverage. Trying to test parts of it have proven tricky, specifically this mailer.smtpTransport.sendMail

var nodemailer = require('nodemailer')

var mailer = {}

mailer.smtpTransport = nodemailer.createTransport('SMTP', {
    'service': 'Gmail',
    'auth': {
        'XOAuth2': {
            'user': '[email protected]',
            'clientId': 'googleClientID',
            'clientSecret': 'superSekrit',
            'refreshToken': '1/refreshYoSelf'
        }
    }
})
var mailOptions = {
    from: 'Some Admin <[email protected]>',
}

mailer.verify = function(email, hash) {
    var emailhtml = 'Welcome to TestCo. <a href="'+hash+'">Click this '+hash+'</a>'
    var emailtxt = 'Welcome to TestCo. This  is your hash: '+hash
    mailOptions.to = email
    mailOptions.subject = 'Welcome to TestCo!'
    mailOptions.html = emailhtml
    mailOptions.text = emailtxt
    mailer.smtpTransport.sendMail(mailOptions, function(error, response){
        if(error) {
            console.log(error)

        } else {
            console.log('Message sent: '+response.message)
        }
    })
}

I'm unsure of how to go about testing, specifically ensuring that my mailer.smtpTransport.sendMail function is passing the correct parameters without actually sending the email. I'm trying to use https://github.com/whatser/mock-nodemailer/tree/master, but I'm probably doing it wrong. Should I be mocking out the method?

var _ = require('lodash')
var should = require('should')
var nodemailer = require('nodemailer')
var mockMailer = require('./helpers/mock-nodemailer')
var transport = nodemailer.createTransport('SMTP', '')

var mailer = require('../../../server/lib/account/mailer')

describe('Mailer', function() {
    describe('.verify()', function() {
        it('sends a verify email with a hashto an address when invoked', function(done) {
            var email ={
                'to': '[email protected]',
                'html': 'Welcome to Testco. <a href="bleh">Click this bleh</a>',
                'text': 'Welcome to Testco. This  is your hash: bleh',
                'subject': 'Welcome to Testco!'
            }

            mockMailer.expectEmail(function(sentEmail) {
            return _.isEqual(email, sentEmail)
            }, done)
            mailer.verify('[email protected]','bleh')
            transport.sendMail(email, function() {})
    })
})

Answer 1

You can use a 'Stub' transport layer on your test instead of SMTP.

var stubMailer = require("nodemailer").createTransport("Stub"),
    options = {
        from: "[email protected]",
        to: "[email protected]",
        text: "My Message!"
    };

   stubMailer.sendMail(options, function(err, response){
     var message = response.message;
   })

So, in that case, 'message' will be the email in text format. Something like this:

MIME-Version: 1.0
X-Mailer: Nodemailer (0.3.43; +http://www.nodemailer.com/)
Date: Fri, 25 Feb 2014 11:11:48 GMT
Message-Id: <123412341234.e23232@Nodemailer>
From: [email protected]
To: [email protected]
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

My Message!

For more examples, take a look at nodemailer test suite: https://github.com/andris9/Nodemailer/blob/master/test/nodemailer-test.js

Answer 2

You can directly mock the sendMail function but it's not obvious how to access it from the tests. A Mailer instance is returned when you create a transport so you need to directly import that class in to your test.

const Mailer = require('nodemailer/lib/mailer')

Then you can mock or stub the sendMail method on the prototype in the usual way. Using Jasmine, you can do it like this:

beforeEach(function () {
  spyOn(Mailer.prototype, 'sendMail').and.callFake(function (mailOptions, cb) {
    cb(null, true)
  })
})

The callFake ensures that the sendMail's callback is still executed encase you need to test what happens next. You can easily simulate an error by passing a first argument to cb: cb(new Error('Email failed'))

Now that the mock is set up, you can check everything is working as intended:

expect(Mailer.prototype.sendMail).toHaveBeenCalled()

Answer 3

expectEmail simply hooks into the transport layer, and expects you to identify the email ( return true if this is the email you are expecting ) by looking at the sentEmail contents.

In this case, return sentEmail.to === '[email protected]' should suffice.

Keep in mind however, this module was designed in an environment where tests are ran in a random order and concurrently. You should propably randomize your data heavily to prevent collisions and false positives. BTW we use something like: var to = Date.now().toString(36) + Faker.Internet.email();