小型测试在没有副作用的纯功能上是脆弱的

Question

我正在做一个RomanNumerals kata，作为我的工具的调整，因为我下周将加入一个Rails项目(耶！(，但我写的测试随机失败(boo！(。

• 每次我让它们运行时，在不对代码进行任何更改的情况下，我都会得到不同的结果
• 我使用rails test作为命令
• 这些版本刚从网上传出来。来自rails new的所有东西都没有任何额外的宝石。(Ruby 2.7.0，Rails 6.0.3(

并行运行的测试和被其他测试覆盖的一些变量之间似乎有一些奇怪的混合。或者可能有一些奇怪的优化事情涉及缓存？

Running via Spring preloader in process 18166
Run options: --seed 29967
# Running:
.......F
Failure:
RomanNumeralHelperTest#test_18_returns_XVIII [/home/eric/rails/rome/test/helpers/roman_numeral_helper_test.rb:55]:
Expected: "XVIII"
  Actual: "IXVIII"

rails test test/helpers/roman_numeral_helper_test.rb:54
........
Finished in 0.066531s, 240.4883 runs/s, 240.4883 assertions/s.
16 runs, 16 assertions, 1 failures, 0 errors, 0 skips

Running via Spring preloader in process 18195
Run options: --seed 59433
# Running:
.............F
Failure:
RomanNumeralHelperTest#test_15_returns_XV [/home/eric/rails/rome/test/helpers/roman_numeral_helper_test.rb:51]:
Expected: "XV"
  Actual: "IXV"

rails test test/helpers/roman_numeral_helper_test.rb:50
..
Finished in 0.053298s, 300.2008 runs/s, 300.2008 assertions/s.
16 runs, 16 assertions, 1 failures, 0 errors, 0 skips

Running via Spring preloader in process 18247
Run options: --seed 14645
# Running:
................
Finished in 0.048711s, 328.4691 runs/s, 328.4691 assertions/s.
16 runs, 16 assertions, 0 failures, 0 errors, 0 skips

class RomanNumeralHelperTest < ActiveSupport::TestCase
  test "1 returns I" do
    assert_equal "I", RomanNumeralHelper.convert(1)
  end  
  test "2 returns II" do
    assert_equal "II", RomanNumeralHelper.convert(2)
  end  
  
  test "3 returns III" do
    assert_equal "III", RomanNumeralHelper.convert(3)
  end
  # Intermittent tests omitted. They go from 1 to 20.
  test "20 returns XX" do
    assert_equal "XX", RomanNumeralHelper.convert(20)
  end
end

module RomanNumeralHelper
  ROMAN_ONE = "I"
  ROMAN_FIVE = "V"
  ROMAN_TEN = "X"
  def self.convert(number)
    result = ""
    current_numeral = ""
    remaining_number = number    
    until remaining_number == 0 do
      if remaining_number > 8
        current_numeral = ROMAN_TEN
        remaining_number -= 10
      elsif remaining_number > 3
        current_numeral += ROMAN_FIVE
        remaining_number -= 5
      else
        result += ROMAN_ONE * remaining_number
        remaining_number = 0
      end      
      if remaining_number < 0
        current_numeral.prepend(ROMAN_ONE)
        remaining_number = 0
      end      
      result += current_numeral
      current_numeral = ""
    end    
    result
  end
end

Answer 1

我的错误是修改了一个常量。

current_numeral = ROMAN_TEN

current_numeral.prepend(ROMAN_ONE)

我更改了ROMAN_TEN引用的字符串。修复方法是：

ROMAN_TEN = "X".freeze

和

current_numeral = ROMAN_TEN.dup

同时使用rubocop——即使是在这样的小项目上——也会给我一个警告。