foo.rb

before(:each) do
  ENV['SITE_DOMAIN'] = 'periscopedata.com'
end

after(:each) do
  ENV.delete('SITE_DOMAIN')
  ActionMailer::Base.deliveries.clear
end

def send_queued_mail_and_expect_subject_to_be(expected_subject)
  expect(Delayed::Job.count).to eq(1)
  Delayed::Job.first.invoke_job
  mail = ActionMailer::Base.deliveries.last
  expect(mail.to).to eq(['engineering+"[email protected]"@periscopedata.com'])
  expect(mail.from).to eq(['[email protected]'])
  expect(mail.subject.include?(expected_subject)).to be(true)
end