Rails 5 - testing the application mailer - ruby-on-rails

Question

I want to test the mailer in my application to make sure it is doing what I want it to do.
class LessonMailer < ApplicationMailer
def send_mail(lesson)
#lesson = lesson
mail(to: lesson.student.email,
subject: 'A lesson has been recorded by your tutor')
end
end
This is my test in the spec/mailers directory
require "rails_helper"
RSpec.describe LessonMailer, :type => :mailer do
describe "lesson" do
let( :student ){ FactoryGirl.create :user, role: 'student', givenname: 'name', sn: 'sname', email: 'test#sheffield.ac.uk' }
let( :lesson ){ FactoryGirl.create :lesson, student_id: 2 }
let( :mail ){ LessonMailer.send_mail( lesson ).deliver_now
it "renders the headers" do
expect(mail.subject).to eq("A lesson has been recorded")
expect(mail.to).to eq(["to#example.ac.uk"])
expect(mail.from).to eq(["no-reply#example.ac.uk"])
end
it "renders the body" do
expect(mail.body.encoded).to match("A lesson form has been recorded")
end
end
end
I want to test that the 'send_mail' method is working the way I want it to however, I am getting this error. How do I go about solving this problem ? Thank you.
NoMethodError:
undefined method `email' for nil:NilClass
# ./app/mailers/lesson_mailer.rb:4:in `send_mail'

Answer 1

So, with FactoryGirl, you just need to instantiate the different objects that you need. Reading your code, it seems clear that a lesson has a student and that students have an email. So go ahead and create everything you need and then call your method. You can do something like this:
# Here's the student factory (for this use case, you'll probably want to make it more general)
FactoryGirl.define do
factory :user do
role 'student'
givenname 'name'
sn 'sname'
email 'test#sheffield.ac.uk'
end
end
# Here's your test
require "rails_helper"
RSpec.describe LessonMailer, :type => :mailer do
describe "lesson" do
let( :student ){ create :student, email: 'test_email#example.com' }
let( :lesson ){ create :lesson, student: student }
let( :mail ){ LessonMailer.send_mail( lesson ) }
it ' ... ' do
...
end
end
end
You'll need to let the test environment know that you want the emails to be delivered to the ActionMailer::Base.deliveries array. To do this, make sure that
config.action_mailer.delivery_method = :test
is set in your config/environments/test.rb
One last thing, I'm not sure if you'll need it, but you might have to call the mailer with, .deliver_now.
Like this:
let( :mail ){ LessonMailer.send_mail( lesson ).deliver_now }
... or it may not send. I can't remember off the top.
Let me know how it goes.