require File.expand_path(File.dirname(__FILE__) + '/edgecase') class AboutInheritance < EdgeCase::Koan class Dog attr_reader :name def initialize(name) @name = name end def bark "WOOF" end end class Chihuahua < Dog def wag :happy end def bark "yip" end end def test_subclasses_have_the_parent_as_an_ancestor assert_equal __, Chihuahua.ancestors.include?(Dog) end def test_all_classes_ultimately_inherit_from_object assert_equal __, Chihuahua.ancestors.include?(Object) end def test_subcases_inherit_behavior_from_parent_class chico = Chihuahua.new("Chico") assert_equal __, chico.name end def test_subclasses_add_new_behavior chico = Chihuahua.new("Chico") assert_equal __, chico.wag assert_raise(___) do fido = Dog.new("Fido") fido.wag end end def test_subclasses_can_modify_existing_behavior chico = Chihuahua.new("Chico") assert_equal __, chico.bark fido = Dog.new("Fido") assert_equal __, fido.bark end # ------------------------------------------------------------------ class BullDog < Dog def bark super + ", GROWL" end end def test_subclasses_can_invoke_parent_behavior_via_super ralph = BullDog.new("Ralph") assert_equal __, ralph.bark end # ------------------------------------------------------------------ class GreatDane < Dog def growl super.bark + ", GROWL" end end def test_super_does_not_work_cross_method george = GreatDane.new("George") assert_raise(___) do george.growl end end end