RSpec class_spy on Rails Mailer

Question

I am trying to test that a specific mailer class is used when a model is saved. In my model I have:

class Foo < ActiveRecord::Base
  def send_email
    if some_condition
      FooMailer.welcome.deliver_now
    else
      FooBarMailer.welcome.deliver_now
    end
  end
def

In my tests for Foo class I have the following

it 'uses the foo bar mailer' do
  foo_mailer = class_spy(FooMailer)
  subject.send_email
  # some_condition will evaluate to false here, so we'll use the FooMailer
  expect(foo_mailer).to have_received :welcome
end

When I run this test it fails with:

(ClassDouble(FooMailer) (anonymous)).welcome(*(any args))
       expected: 1 time with any arguments
       received: 0 times with any arguments

Answer 1

The issue would seem to be that you haven't swapped out the current definition of your mailer class with the spy, so your spy isn't receiving any messages. To replace it, you would use the stub_const method:

it 'uses the foo bar mailer' do
  foobar_mailer = class_spy(FooBarMailer)
  stub_const('FooBarMailer', foobar_mailer)
  subject.send_email
  # some_condition will evaluate to false here, so we'll use the FooBarMailer
  expect(foobar_mailer).to have_received :welcome
end

Answer 2

foo_mailer = class_spy(FooMailer).as_stubbed_const