ruby-on-rails – 在Rails中为什么我的邮件正文只在我的测试中空

我的邮件类：

class TermsMailer < ApplicationMailer
  default from: "info@domain.com"
  def notice_email(user,filename)
    @user = user
    @file = filename
    mail(to: "info@domain.com",subject: 'Data downloaded')
  end
end

我的测试：

require 'test_helper'

class TermsMailerTest < ActionMailer::TestCase
  test "notice" do
    email = TermsMailer.notice_email(users(:me),'file.ext').deliver_now
    assert_not ActionMailer::Base.deliveries.empty?
    assert_equal ['info@domain.com'],email.from
    assert_equal ['info@domain.com'],email.to
    assert_equal 'Data downloaded',email.subject
    assert_equal 'arbitrary garbage for comparison',email.body.to_s
  end
end

这个邮件程序的视图不是空白的,实际上是在电子邮件中发送正确的内容.那么为什么我的测试中的电子邮件正文空白？