正确调用其他方法的TDD方法

Question

我需要一些TDD概念的帮助.说我有以下代码

def execute(command)
  case command
  when "c"
    create_new_character
  when "i"
    display_inventory
  end
end

def create_new_character
  # do stuff to create new character
end

def display_inventory
  # do stuff to display inventory
end

现在我不确定要为我的单元测试编写什么.如果我为该execute方法编写单元测试并不能完全覆盖我的测试create_new_character和display_inventory？或者我在那时测试错误的东西？我对该execute方法的测试是否只测试执行是否传递给正确的方法并停在那里？然后,我应该写更多的单元测试是专门测试create_new_character和display_inventory？

Answer 1

我推测,因为你提到TDD,所讨论的代码实际上并不存在.如果它确实那么你没有做真正的TDD而是TAD(开发后测试),这自然会引发诸如此类的问题.在TDD中,我们从测试开始.您似乎正在构建某种类型的菜单或命令系统,因此我将以此为例.

describe GameMenu do
  it "Allows you to navigate to character creation" do
    # Assuming character creation would require capturing additional
    # information it violates SRP (Single Responsibility Principle)
    # and belongs in a separate class so we'll mock it out.
    character_creation = mock("character creation")
    character_creation.should_receive(:execute)

    # Using constructor injection to tell the code about the mock
    menu = GameMenu.new(character_creation)
    menu.execute("c")
  end
end

这个测试会导致一些类似于以下的代码(记住,只需要足够的代码来使测试通过,不再需要)

class GameMenu
  def initialize(character_creation_command)
    @character_creation_command = character_creation_command
  end

  def execute(command)
    @character_creation_command.execute
  end
end

现在我们将添加下一个测试.

it "Allows you to display character inventory" do
  inventory_command = mock("inventory")
  inventory_command.should_receive(:execute)
  menu = GameMenu.new(nil, inventory_command)
  menu.execute("i")
end

运行此测试将引导我们实现如下:

class GameMenu
  def initialize(character_creation_command, inventory_command)
    @inventory_command = inventory_command
  end

  def execute(command)
    if command == "i"
      @inventory_command.execute
    else
      @character_creation_command.execute
    end
  end
end

这个实现引导我们对我们的代码提出疑问.输入无效命令时我们的代码应该怎么做？一旦我们确定了该问题的答案,我们就可以实施另一项测试.

it "Raises an error when an invalid command is entered" do
  menu = GameMenu.new(nil, nil)
  lambda { menu.execute("invalid command") }.should raise_error(ArgumentError)
end

这驱逐了对execute方法的快速改变

  def execute(command)
    unless ["c", "i"].include? command
      raise ArgumentError("Invalid command '#{command}'")
    end

    if command == "i"
      @inventory_command.execute
    else
      @character_creation_command.execute
    end
  end

现在我们已经通过了测试,我们可以使用Extract Method重构将命令的验证提取到Intent Revealing方法中.

  def execute(command)
    raise ArgumentError("Invalid command '#{command}'") if invalid? command

    if command == "i"
      @inventory_command.execute
    else
      @character_creation_command.execute
    end
  end

  def invalid?(command)
    !["c", "i"].include? command
  end

现在我们终于找到了解决问题的重点.由于该invalid?方法是通过重构现有的测试代码来驱逐的,因此不需要为它编写单元测试,它已经被覆盖并且不能独立存在.由于库存和字符命令未经我们现有的测试测试,因此需要独立进行测试驱动.

请注意,我们的代码可能会更好,所以当测试通过时,让我们更清楚一点.条件语句是我们违反OCP(开放 - 封闭原则)的指标,我们可以使用替换条件多态重构来删除条件逻辑.

# Refactored to comply to the OCP.
class GameMenu
  def initialize(character_creation_command, inventory_command)
    @commands = {
      "c" => character_creation_command,
      "i" => inventory_command
    }
  end

  def execute(command)
    raise ArgumentError("Invalid command '#{command}'") if invalid? command
    @commands[command].execute
  end

  def invalid?(command)
    !@commands.has_key? command
  end
end

现在我们重构了这个类,这样一个额外的命令只需要我们在命令哈希中添加一个额外的条目,而不是改变条件逻辑和invalid?方法.

所有的测试仍然应该通过,我们几乎完成了我们的工作.一旦我们测试了驱动单个命令,你就可以回到initialize方法并为命令添加一些默认值,如下所示:

  def initialize(character_creation_command = CharacterCreation.new,
                 inventory_command = Inventory.new)
    @commands = {
      "c" => character_creation_command,
      "i" => inventory_command
    }
  end

最后的测试是:

describe GameMenu do
  it "Allows you to navigate to character creation" do
    character_creation = mock("character creation")
    character_creation.should_receive(:execute)
    menu = GameMenu.new(character_creation)
    menu.execute("c")
  end

  it "Allows you to display character inventory" do
    inventory_command = mock("inventory")
    inventory_command.should_receive(:execute)
    menu = GameMenu.new(nil, inventory_command)
    menu.execute("i")
  end

  it "Raises an error when an invalid command is entered" do
    menu = GameMenu.new(nil, nil)
    lambda { menu.execute("invalid command") }.should raise_error(ArgumentError)
  end
end

决赛GameMenu看起来像:

class GameMenu
  def initialize(character_creation_command = CharacterCreation.new,
                 inventory_command = Inventory.new)
    @commands = {
      "c" => character_creation_command,
      "i" => inventory_command
    }
  end

  def execute(command)
    raise ArgumentError("Invalid command '#{command}'") if invalid? command
    @commands[command].execute
  end

  def invalid?(command)
    !@commands.has_key? command
  end
end

希望有所帮助!

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