src/about_inheritance.rb

   1 require File.expand_path(File.dirname(__FILE__) + '/edgecase')
   2
   3 class AboutInheritance < EdgeCase::Koan
   4   class Dog
   5     attr_reader :name
   6
   7     def initialize(name)
   8       @name = name
   9     end
  10
  11     def bark
  12       "WOOF"
  13     end
  14   end
  15
  16   class Chihuahua < Dog
  17     def wag
  18       :happy
  19     end
  20
  21     def bark
  22       "yip"
  23     end
  24   end
  25
  26   def test_subclasses_have_the_parent_as_an_ancestor
  27     assert_equal __(true), Chihuahua.ancestors.include?(Dog)
  28   end
  29
  30   def test_all_classes_ultimately_inherit_from_object
  31     assert_equal __(true), Chihuahua.ancestors.include?(Object)
  32   end
  33
  34   def test_subclasses_inherit_behavior_from_parent_class
  35     chico = Chihuahua.new("Chico")
  36     assert_equal __("Chico"), chico.name
  37   end
  38
  39   def test_subclasses_add_new_behavior
  40     chico = Chihuahua.new("Chico")
  41     assert_equal __(:happy), chico.wag
  42
  43     assert_raise(___(NoMethodError)) do
  44       fido = Dog.new("Fido")
  45       fido.wag
  46     end
  47   end
  48
  49   def test_subclasses_can_modify_existing_behavior
  50     chico = Chihuahua.new("Chico")
  51     assert_equal __("yip"), chico.bark
  52
  53     fido = Dog.new("Fido")
  54     assert_equal __("WOOF"), fido.bark
  55   end
  56
  57   # ------------------------------------------------------------------
  58
  59   class BullDog < Dog
  60     def bark
  61       super + ", GROWL"
  62     end
  63   end
  64
  65   def test_subclasses_can_invoke_parent_behavior_via_super
  66     ralph = BullDog.new("Ralph")
  67     assert_equal __("WOOF, GROWL"), ralph.bark
  68   end
  69
  70   # ------------------------------------------------------------------
  71
  72   class GreatDane < Dog
  73     def growl
  74       super.bark + ", GROWL"
  75     end
  76   end
  77
  78   def test_super_does_not_work_cross_method
  79     george = GreatDane.new("George")
  80     assert_raise(___(NoMethodError)) do
  81       george.growl
  82     end
  83   end
  84
  85 end