ruby-on-rails – RSpec：测试邮件程序只调用一次

class EventMailer < BaseMailer
  def event_added(user_id,event_id)
    # do stuff and email user about the event
  end
end

我在Event类中调用了这个EventMailer：

class Event < Task
  def notify_by_email(user)
    EmailLog.send_once(user.id,id) do
      EventMailer.delay(queue: 'mailer').event_added(user.id,id)
    end
  end
end

EmailLog是一个记录已发送电子邮件的类. .delay由Sidekiq添加.

但是当我尝试测试每个事件和用户只调用一次#notify_by_email时,我的规范失败了：

1) Event#notify_by_email only sends once per user
     Failure/Error: expect(EventMailer).to receive(:event_added).once
       (<EventMailer (class)>).event_added(any args)
           expected: 1 time with any arguments
           received: 0 times with any arguments

规范如下：

let(:owner) { User.make! }
let(:product) { Product.make! }
let(:event) { Task.make!(user: owner,product: product) }

describe '#notify_by_email' do
  before do
    EventMailer.stub(:delay).and_return(EventMailer)
  end

  it 'only sends once per user' do
    event.notify_by_email(owner)
    event.notify_by_email(owner)

    expect(EventMailer).to receive(:event_added).once
  end
end

有关此规范失败的原因以及我如何修复它的任何见解？奇怪的是,如果我将一个puts语句放在传递给EmailLog.send_once的块中,它只打印一次,规范仍然报告没有调用EventMailer.event_added.