有没有一种干净的方法来测试Rspec中的ActiveRecord回调？

Question

假设我有以下ActiveRecord类：

class ToastMitten < ActiveRecord::Base
  before_save :brush_off_crumbs
end

是否有一种干净的方式来测试:brush_off_crumbs是否已被设置为before_save回调？

“干净”是指：

1. “没有实际保存”，因为
   • 这很慢
   • 我不需要正确测试ActiveRecord 处理 before_save指令;我需要测试我是否正确告诉它在保存之前该做什么。
2. “不通过无证方法进行黑客攻击”

我找到了一种满足标准＃1但不满足＃2的方法：

it "should call have brush_off_crumbs as a before_save callback" do
  # undocumented voodoo
  before_save_callbacks = ToastMitten._save_callbacks.select do |callback|
    callback.kind.eql?(:before)
  end

  # vile incantations
  before_save_callbacks.map(&:raw_filter).should include(:brush_off_crumbs)
end

Answer 1

使用run_callbacks

这不那么黑客，但并不完美：

it "is called as a before_save callback" do
  revenue_object.should_receive(:record_financial_changes)
  revenue_object.run_callbacks(:save) do
    # Bail from the saving process, so we'll know that if the method was 
    # called, it was done before saving
    false 
  end
end

使用此技术测试after_save会更加尴尬。