Test ActionMailer deliver_later
in RSpec Controller Tests
it "sends email notification" do
NotificationMailer.admin_new_update_mail(admin.id, update.id).deliver_now
expect(ActionMailer::Base.deliveries.count).to eq(1)
mail = ActionMailer::Base.deliveries.last
expect(mail.to).to eq([admin.email])
expect(mail.subject).to eq('New update created on Teamitup')
end