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Moses Gathuku
Moses Gathuku

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Testing Action Mailer in Rails

Rails provide us with useful test helpers to ActionMailer which helps to easily iterate our design, test if our code queues the right email and our email contains the right content.

Getting Started

After creating a rails app we can generate a new Mailer in our app.

rails generate mailer NotificationMailer
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With the above command we generate a mailer named NotificationMailer, this creates:-

  1. A class NotificationMailer in app/mailers directory.
  2. A class NotificationMailerTest in test/mailers/notification_mailer_test.rb
  3. A preview class NotificationMailerPreview in test/mailer/preview/notificaton_mailer_preview.rb
  4. A view directory notification_mailer in app/views

Mailer Logic

We are ready to create our first email. To create an email that is sent when users sign up in your application head to NotificationMailer in app/mailer

class NotificationMailer < ApplicationMailer
  default from: ''

  def welcome(user)
    @user = user
    mail(to:, subject: 'Welcome to my App')
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We have defined a welcome method that sends a welcome email. The method accepts the user object as the argument.

Note we have defined the default from at the top of our class.

Mailer view

After writing our logic remember notification_mailer directory that was created in our app/view, head into the directory and create a file named welcome.erb.html. The file will render HTML design for our email.

Note the naming convention. The name must match the name of our email method.

<!-- <!DOCTYPE html>
<html lang="en" dir="ltr">
    <meta charset="utf-8">

    <h1>Thanks for signing,<%= %> </h1>
    <p>Welcome to the app</p>
</html> -->
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Mailer Preview

Remember the preview file that was created? Mailer preview enables us to preview our email design. This is helpful since we don't have to send the actual email to see our email design.
All we need is to define a method that implements our mailer. notification_mailer_preview.rb

class NotificationMailerPreview < ActionMailer::Preview
  def welcome
    user = User.first
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After this ensure your server is running and navigate to route http://localhost:3000/rails/mailers. All your mailers and specific email methods will be listed. Click welcome to view the welcome email design.


Your mailers class just like any other part of Rails application should be tested to ensure they are working properly.
Why should you test your mailers? below are some of the reasons.

  • To ensure that emails are being processed (created and sent).
  • To ensure that the email content is correct (subject, sender, body, etc).
  • To ensure the right emails are being sent at the right times.

There are two aspects of testing mailers.

  • Units tests
  • Functional tests

Units tests

In unit tests, we run the mailer in isolation with tightly controlled inputs and compare the output to a known value (a fixture.)
In our NotificationMailer we have welcome action which is used to send a welcome email when users sign up. Below is the unit test.

 # frozen_string_literal: true

require 'test_helper'

class NotificationMailerTest < ActionMailer::TestCase

  def setup
    @user = users(:one)

  test 'welcome' do
    email = NotificationMailer.welcome(@user)
    assert_emails 1 do

    assert_equal, []
    assert_equal email.from, ['']
    assert_equal email.subject, 'Welcome to my App'
    assert_match 'Thanks for signing', email.body.encoded
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In the test above, we create the email and store the returned object in the email variable. We then ensure that it was sent (the first assert), then, in the second batch of assertions, we ensure that the email does indeed contain what we expect.


To understand more about mailers. The line ActionMailer::Base.delivery_method = :test in config/environments/test.rb sets the delivery method to test mode so that email will not be delivered (useful to avoid spamming your users while testing) but instead, it will be appended to an array (ActionMailer::Base.deliveries)

You can clear the deliveries array with ActionMailer::Base.deliveries.clear

Top comments (1)

naigueldev profile image

Very good! You helped me a lot. Thanks Moses ;)