Rails / RSpec：如何测试#initialize方法？

Question

如何使用 RSpec 指定 #initialize 行为？例如这里：

generator.rb

class Generator
  attr_accessor :seed

  def initialize(seed = nil)
    @seed = seed || pick_seed
  end

  def pick_seed
    Time.now.to_i
  end
end

generator_spec.rb

require 'generator'

describe Generator

  it "calls 'pick_seed' method unless seed specified" do
  end

end

我想设定期望 pick_seed 方法从 #initialize 方法调用。

Answer 1

对我来说，期望是设计协作者之间的对话。所以，您必须决定 - #pick_seed 是内部实现细节还是协作角色接口的一部分？

如果pick_seed 是一个实现细节，则期望是该工作的错误工具。而且，由于您有一个种子访问器，因此您可以继续进行（注意每个示例一个断言）：

class Generator
  attr_accessor :seed

  def initialize(seed = nil)
    @seed = seed || pick_seed
  end

  def pick_seed
    Time.now.to_i
  end
end

describe Generator do
  context "creating" do 
    context "when a seed is specified" do
      it "uses that seed" do
        seed = 123
        generator = Generator.new(seed)
        generator.seed.should == seed
      end
    end
    context "when a seed is not specified" do
      it "creates its own seed" do
        generator = Generator.new
        generator.seed.should_not be_nil
      end
    end
  end
end

OTOH，如果选择种子是“种子选择器”角色的一部分，那么模拟在设计种子选择器时很有价值，并且依赖注入是分配角色的标准方法。你可以这样写：

class GeneratorWithCollaborator
  attr_accessor :seed

  def initialize(seed = nil, seed_picker = self)
    @seed = seed || seed_picker.pick_seed
  end

  def pick_seed
    Time.now.to_i
  end
end

describe GeneratorWithCollaborator do
  context "creating" do
    context "when a seed is specified" do
      it "uses that seed" do
        seed = 123
        seed_picker = double('seed picker')
        seed_picker.should_not_receive(:pick_seed)
        generator = GeneratorWithCollaborator.new(seed, seed_picker)
        generator.pick_seed
      end
    end

    context "when a seed is not specified" do
      it "delegates to its seed picker" do
        seed_picker = double('seed picker')
        seed_picker.should_receive(:pick_seed)
        generator = GeneratorWithCollaborator.new(nil, seed_picker)
      end
    end
  end
end