Rails - How do you test ActionMailer sent a specific email in tests

Question

Currently in my tests I do something like this to test if an email is queued to be sent

assert_difference(\'ActionMailer::Base.deliveries.size\', 1) do              


        

Answer 1

As of 2020 (Rails 6 era, probably introduced earlier) you can do the following: (using a SystemTest example) TL;DR: use assert_emails from ActionMailer::TestHelper and ActionMailer::Base.deliveries.last to access the mail itself.

require "application_system_test_case"
require 'test_helper'
require 'action_mailer/test_helper'

class ContactTest < ApplicationSystemTestCase
  include ActionMailer::TestHelper

  test "Send mail via contact form on landing page" do
    visit root_url

    fill_in "Message", with: 'message text'

    # Asserting a mail is sent
    assert_emails 1 do
      click_on "Send"
    end

    # Asserting stuff within that mail
    last_email  = ActionMailer::Base.deliveries.last

    assert_equal ['whatever'], last_email.reply_to
    assert_equal "contact", last_email.subject
    assert_match /Mail from someone/, last_email.body.to_s
  end
end

Official doc:

• ActionMailer Guide/Testing
• Testing Guide/ActionMailer

Note Instead of manually checking the content of the mail as in the system test above, you can also test whether a specific mailer action was used, like this:

assert_enqueued_email_with ContactMailer, :welcome, args: ["Hello", "Goodbye"]

And some other handy assertion, see https://api.rubyonrails.org/v6.0.3.2/classes/ActionMailer/TestHelper.html#method-i-assert_emails .