Add testing example

testing/01_testing.md

@@ -1,2 +1,8 @@
-!SLIDE
+!SLIDE subsection
 # Testing
+
+
+!SLIDE
+# Unit::Test
+
+### See `tag_list.rb`

testing/tag_list.rb

@@ -0,0 +1,87 @@
+class TagList
+  include Enumerable
+
+  attr_reader :tags
+
+  def initialize
+    @tags = []
+  end
+
+  def add(tag)
+    @tags << tag
+    @tags.uniq!
+    self
+  end
+
+  def remove(tag)
+    @tags.delete_if { |t| t == tag }
+    self
+  end
+
+  def each(&block)
+    @tags.each(&block)
+  end
+end
+
+
+if __FILE__ == $0
+
+  require 'test/unit'
+
+  class TagListTest < Test::Unit::TestCase
+    def setup
+      @i = TagList.new
+    end
+
+    def test_implements_enumerable
+      assert TagList.ancestors.include?(Enumerable)
+      assert TagList.public_instance_methods.include?(:each)
+    end
+
+    def test_initialize_requires_no_parameters
+      assert_raise(ArgumentError) { TagList.new([]) }
+      assert_nothing_raised { TagList.new }
+    end
+
+    def test_initialize_initializes_tags
+      i = TagList.new
+      assert_equal [], i.tags
+    end
+
+    def test_add_adds_a_tag
+      assert_equal [], @i.tags
+      @i.add("one")
+      assert_equal ["one"], @i.tags
+      @i.add("two")
+      assert_equal ["one", "two"], @i.tags
+    end
+
+    def test_add_filters_duplicate_tags
+      @i.add("one")
+      assert_equal ["one"], @i.tags
+      @i.add("one")
+      assert_equal ["one"], @i.tags
+    end
+
+    def test_add_returns_self
+      assert_equal @i, @i.add("tag")
+    end
+
+    def test_remove_removes_a_tag_if_tag_exists
+      %w( one two ).each { |tag| @i.add(tag) }
+      @i.remove("one")
+      assert_equal ["two"], @i.tags
+    end
+
+    def test_remove_does_not_do_anything_if_tag_does_not_exist
+      %w( one two ).each { |tag| @i.add(tag) }
+      @i.remove("three")
+      assert_equal ["one", "two"], @i.tags
+    end
+
+    def test_remove_returns_self
+      assert_equal @i, @i.remove("tag")
+    end
+  end
+
+end