hash - 尝试模拟哈希元素的获取和放置时，RSpec 无法定义单例错误

Question

我有一个图书模型，它是一个 ruby​​ 脚本，可将价格分配给程序中提到的某些预定义图书标题。这是书本模型的外观:-

class Book

  attr_accessor :books  
  def initialize books
    puts "Welcome to setting book price program"
    @books = books
  end

  def get_prices
    puts "Please enter appropriate price for each book item:-"
    count = 0
    @books = @books.inject({}) { |hash, book|
      print "#{book.first}: "
      price = STDIN.gets.chomp
      while (price !~ /^[1-9]\d*$/ && price != "second hand")
        puts "Price can't be 0 or a negative integer or in decimal format or alphanumeric. \nPlease input appropriate price in integer"
        price = STDIN.gets.chomp #gets.chomp - throws error
      end
      price == "second hand" ? price = "100" : price #takes a default price
      hash[book.first] = price.to_i
      hash
    }
  end

end

books = {"The Last Samurai" => nil,
         "Ruby Cookbook" =>  nil,
         "Rails Recipes" =>  nil,
         "Agile Development with Rails" =>  nil,
         "Harry Potter and the Deathly Hallows" =>  nil}


book_details = Book.new(books)
book_details.get_prices
puts "\n*******Books Details:#{book_details.books}******\n"

我正在尝试编写一个测试用例来检查每本书的价格输入是否正确。如果价格输入不正确，它应该要求用户重新输入正确的价格。该程序做得很好。但是当我尝试使用 RSpec 模拟这种行为时，我遇到了困难。

require 'spec_helper'

describe Book do

  before :each do
    books = {"The Last Samurai" => nil,
         "Ruby Cookbook" =>  nil,
         "Rails Recipes" =>  nil,
         "Agile Development with Rails" =>  nil,
         "Harry Potter and the Deathly Hallows" =>  nil}
    @book = Book.new(books)
  end

  describe "#new" do
    it "Should be an instance of the Book" do
      @book.should be_an_instance_of Book
    end
  end

  describe "#getprice" do
    it "Should get the price in the correct format or else return appropriate error" do
      puts "\n************************************************************************\n"
      book_obj = @book
      STDOUT.should_receive(:puts).and_return("Welcome to setting book price program")
      book_obj.get_prices.should_not be_nil
      book_obj.books["The Last Samurai"].stub!(:gets) {"40"} #trying to set the value for one book using Hash
      book_obj.books["The Last Samurai"].should == 40 #verifying the value set for a particular key is accurate
    end
  end

end

你甚至可以 clone this code从 Github 开始尝试这个。我正在使用 Ruby 1.9.3 和 rspec 2.11.0

The error that I'm getting currently is:-

Failures:

  1) Book#getprice Should get the price in the correct format or else return appropriate error
     Failure/Error: book_obj.books["The Last Samurai"].stub!(:gets) {"40"} #trying to set the value for one book using Hash
     TypeError:
       can't define singleton
     # ./spec/book_spec.rb:31:in `block (3 levels) in <top (required)>'

Finished in 7.61 seconds
2 examples, 1 failure

Failed examples:

rspec ./spec/book_spec.rb:21 # Book#getprice Should get the price in the correct format or else return appropriate error

更新问题

对于错误的用户输入，使用以下测试用例，我收到以下错误。我怎样才能正确处理这个？我尝试了几个选项，但它们似乎都失败了。请参阅作为规范片段一部分的每个选项的注释。

 it "Incorrect input format should return error message asking user to re input" do
      puts "\n************************************************************************\n"
      book_obj = @book
      STDIN.stub(:gets) { "40abc" }

      #book_obj.get_prices.should be_nil --> adding this line of code goes into an infinite loop with the error message below
      #Price cannot be 0 or a negative integer or in decimal format or alphanumeric. \nPlease input appropriate duration in integer\n

      STDOUT.should_receive(:puts).and_return("Price cannot be 0 or a negative integer or in decimal format or alphanumeric. \nPlease input appropriate duration in integer\n")

      #the below two tests fails with syntax error - don't seem that easy to figure out what's going wrong

      #STDOUT.should_receive("Price cannot be 0 or a negative integer or in decimal format or alphanumeric. \nPlease input appropriate duration in integer\n")
      #STDOUT.should == "Price cannot be 0 or a negative integer or in decimal format or alphanumeric. \nPlease input appropriate duration in integer\n"
    end


Failures:

  1) Book#getprice Incorrect input format should return error message asking user to re input
     Failure/Error: STDOUT.should_receive(:puts).and_return("Price cannot be 0 or a negative integer or in decimal format or alphanumeric. \nPlease input appropriate duration in integer\n")
       (#<IO:0x00000001c7b298>).puts(any args)
           expected: 1 time
           received: 0 times
     # ./spec/book_spec.rb:40:in `block (3 levels) in <top (required)>'

我真的很感激任何指导如何做到这一点。谢谢你。

Answer 1

如果您使用 --backtrace 标志运行规范，您会看到在 https://github.com/rspec/rspec-mocks/blob/v2.13.0/lib/rspec/mocks/method_double.rb#L140 上引发了错误，其中 rspec-mocks 试图获取被 stub 或模拟的对象的单例类。这适用于大多数类的实例，但规范中有错误。

代码将 gets 发送到 STDIN ，但规范试图在 gets 上 stub book_obj.books["The Last Samurai"] ，当时是 int ，并且您无法从 int 获得单例:

$ irb
1.9.3-p392 :001 > class << 1; self; end
TypeError: can't define singleton
        from (irb):1
    from /Users/david/.rvm/rubies/ruby-1.9.3-p392/bin/irb:16:in `<main>'

如果我理解正确，您想要进行两个更改。首先，将脚本的最后几行移动到一个单独的文件中，当您运行规范时不会加载该文件，例如bin/books(它可能需要 book.rb 然后添加这些行)。

接下来，删除在 gets 上 stub book_obj.books["The Last Samurai"] 的行，并在调用 gets 的行之前添加一行在 STDIN 上 stub get_prices 的行(这是发生与 STDIN 的交互的时间):

STDIN.stub(:gets) { "40" }
book_obj.get_prices.should_not be_nil

这至少会让你的规范通过。

一般来说，直接处理 STDIN 和 STDOUT 的代码很难在对象级别进行规范，因为像 rspec、minitest 等测试工具都使用 STDOUT 来呈现它们的信息，所以你最终会在贝壳。我建议要么更改设计以将输入/输出流注入(inject) book 类(运行脚本时可以是 STDIN 和 STDOUT，但运行 rspec 时测试 double )，或者使用像 aruba 这样设计的工具指定交互式 shell 脚本。