不使用邮件方法时Rails电子邮件预览

Question

我正在使用Mailgun的Ruby API从标准Rails邮件程序发送电子邮件。但是，由于我没有使用mail方法，因此预览不起作用：

You are trying to preview an email that does not have any content. This is probably because the mail method has not been called

有没有办法在不使用mail方法时预览邮件程序？优选地，不需要宝石的那种。

以下是邮寄的样本：

class SuppliersMailer < ApplicationMailer
  def send_user_details supplier
    @supplier = supplier

    message = Mailgun::MessageBuilder.new
    message.from default_params[:from]
    message.add_recipient :to, "email@example.com", {'first' => "Anna"}
    message.subject "My subject"
    message.set_html_body template_to_html_string("path/to/template")
    message.test_mode(true) if Rails.env.test?

    client.send_message ENV["MAILGUN_DOMAIN"], message
  end

  private

  def client
    Mailgun::Client.new ENV['MAILGUN_KEY']
  end
end

预览课程：

class SuppliersMailerPreview < ActionMailer::Preview
  def send_user_details
    SuppliersMailer.send_user_details supplier
  end

  private

  def supplier
    Supplier.last
  end
end