ruby - ruby 中的结构与测试双重

Question

在结构上使用 rspec double 的优缺点是什么？例如

before :each do
  location = double "locatoin"
  location.stub(:id => 1)
end

对比

before :each do
  location = Struct.new("locatoin", :id)
  location.new.id = 1
end

Answer 1

测试替身更容易设置

Slip = Struct.new(:id)
slip = Slip.new(:id => 1)

对比

slip = double('slip', :id => 1)

测试替身生成更多信息性错误消息

require 'spec_helper'

class TooLongError < StandardError; end

class Boat
  def moor(slip)
    slip.moor!(self)
  rescue TooLongError
    false
  end
end

describe Boat do
  let(:boat) { subject }

  context "when slip won't accept boat" do
    it "can't be moored" do
      Slip = Struct.new('Slip')
      slip = Slip.new
      boat.moor(slip).should be_false
    end
  end
end

Failure/Error: slip.moor!(self)
 NoMethodError:
   undefined method `moor!' for #<struct Struct::Slip >

对比

it "can't be moored" do
  slip = double('slip')
  boat.moor(slip).should be_false
end

Failure/Error: slip.moor!(self)
   Double "slip" received unexpected message :moor! with (#<Boat:0x106b90c60>)

测试替身对测试有更好的支持

class Boat
  def moor(slip)
    slip.dont_care
    slip.moor!(self)
  rescue TooLongError
    false
  end
end

it "can't be moored" do
  Slip = Struct.new('Slip')
  slip = Slip.new
  slip.should_receive(:moor!).and_raise(TooLongError)
  boat.moor(slip).should be_false
end

Failure/Error: slip.dont_care
 NoMethodError:
   undefined method `dont_care' for #<struct Struct::Slip >

对比

it "can't be moored" do
  slip = double('slip').as_null_object
  slip.should_receive(:moor!).and_raise(TooLongError)
  boat.moor(slip).should be_false
end

0 failures # passed!

这只是几个例子——我相信还有更多理由更喜欢测试替身。