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

Answer 1

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()