expect(UserMailer).to receive(UserMailer.addon_purchased).with(event_order_id: @event_order.id)

我正在使用上面的代码。我需要做哪些更改才能使其正常工作？
我的邮件方法

@event_order = EventOrder.find(params[:event_order_id])

    # TECH DEBT: why is .first relevant?
    @ticket = @event_order.addons.first.event_ticket
    if @ticket.blank?
      Rails.logger.error "ticket purchased but no ticket found for Order# - #{@event_order.id}"
      raise StandardError.new("ticket not found")
    end