Current progress

koans/about_inheritance.rb

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+require File.expand_path(File.dirname(__FILE__) + '/neo')
+
+class AboutInheritance < Neo::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_subclasses_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