ruby-on-rails - 如何使用 'assert_difference' 为两个不同的对象断言两个不同的值？

Question

我有以下测试:

it 'create action: a user replies to a post for the first time' do
  login_as user

  # ActionMailer goes up by two because a user who created a topic has an accompanying post.
  # One email for post creation, another for post replies.
  assert_difference(['Post.count', 'ActionMailer::Base.deliveries.size'], 2) do
    post :create, topic_id: topic.id, post: { body: 'Creating a post for the first time.' }
  end
  email = ActionMailer::Base.deliveries

  email.first.to.must_equal [user.email]
  email.subject.must_equal 'Post successfully created'
  must_redirect_to topic_path(topic.id)

  email.last.to.must_equal [user.email]
  email.subject.must_equal 'Post reply sent'
  must_redirect_to topic_path(topic.id)
end

上面的测试由于代码中的 assert_difference block 而中断。为了让这个测试通过，我需要让 Post.count 递增 1，然后让 ActionMailer::Base.deliveries.size 递增 2。该场景将使测试通过。我已尝试将代码重写为第二种类型的测试。

it 'create action: a user replies to a post for the first time' do
  login_as user

  assert_difference('Post.count', 1) do
    post :create, topic_id: topic.id, post: { body: 'Creating a post for the first time.' }
  end

  # ActionMailer goes up by two because a user who created a topic has an accompanying post.
  # One email for post creation, another for post reply.
  assert_difference('ActionMailer::Base.deliveries.size', 2) do
    post :create, topic_id: topic.id, post: { body: 'Creating a post for the first time.' }
  end

  email = ActionMailer::Base.deliveries

  email.first.to.must_equal [user.email]
  email.subject.must_equal 'Post successfully created'
  must_redirect_to topic_path(topic.id)

  email.last.to.must_equal [user.email]
  email.subject.must_equal 'Post reply sent'
  must_redirect_to topic_path(topic.id)
end

第二次迭代接近我想要的但又不完全是。此代码的问题在于，由于 assert_difference block 中的创建调用，它将创建两次 post 对象。我查看了 rails api 指南中的 assert_difference 代码和在此处找到的 api docks(assert_difference API dock 但这不是我需要的。我需要这样的东西:

assert_difference ['Post.count','ActionMailer::Base.deliveries.size'], 1,2 do
   #create a post
end

有没有办法实现它？

Answer 1

你可以像这样嵌套它们:

assert_difference("Post.count", 1) do
  assert_difference("ActionMailer::Base.deliveries.size", 2) do
    # Create a post
  end
end