3. Add an acts_as_yaffle method to ActiveRecord

A common pattern in plugins is to add a method called acts_as_something to models. In this case, you want to write a method called acts_as_yaffle that adds a squawk method to your models.

To keep things clean, create a new test file called acts_as_yaffle_test.rb in your plugin's test directory and require your test helper.

# File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb

require File.dirname(__FILE__) + '/test_helper.rb'

class Hickwall < ActiveRecord::Base
  acts_as_yaffle
end

class ActsAsYaffleTest < Test::Unit::TestCase
end

# File: vendor/plugins/lib/acts_as_yaffle.rb

module Yaffle
end

One of the most common plugin patterns for acts_as_yaffle plugins is to structure your file like so:

module Yaffle
  def self.included(base)
    base.send :extend, ClassMethods
  end

  module ClassMethods
    # any method placed here will apply to classes, like Hickwall
    def acts_as_something
      send :include, InstanceMethods
    end
  end

  module InstanceMethods
    # any method placed here will apply to instaces, like @hickwall
  end
end

With structure you can easily separate the methods that will be used for the class (like Hickwall.some_method) and the instance (like @hickwell.some_method).

Let's add class method named acts_as_yaffle - testing it out first. You already defined the ActiveRecord models in your test helper, so if you run tests now they will fail.

Back in your acts_as_yaffle file, update ClassMethods like so:

module ClassMethods
  def acts_as_yaffle(options = {})
    send :include, InstanceMethods
  end
end

Now that test should pass. Since your plugin is going to work with field names, you need to allow people to define the field names, in case there is a naming conflict. You can write a few simple tests for this:

# File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb

require File.dirname(__FILE__) + '/test_helper.rb'

class ActsAsYaffleTest < Test::Unit::TestCase
  def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
    assert_equal "last_squawk", Hickwall.yaffle_text_field
  end

  def test_a_hickwalls_yaffle_date_field_should_be_last_squawked_at
    assert_equal "last_squawked_at", Hickwall.yaffle_date_field
  end

  def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
    assert_equal "last_tweet", Wickwall.yaffle_text_field
  end

  def test_a_wickwalls_yaffle_date_field_should_be_last_tweeted_at
    assert_equal "last_tweeted_at", Wickwall.yaffle_date_field
  end
end

To make these tests pass, you could modify your acts_as_yaffle file like so:

# File: vendor/plugins/yaffle/lib/acts_as_yaffle.rb

module Yaffle
  def self.included(base)
    base.send :extend, ClassMethods
  end

  module ClassMethods
    def acts_as_yaffle(options = {})
      cattr_accessor :yaffle_text_field, :yaffle_date_field
      self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
      self.yaffle_date_field = (options[:yaffle_date_field] || :last_squawked_at).to_s
      send :include, InstanceMethods
    end
  end

  module InstanceMethods
  end
end

Now you can add tests for the instance methods, and the instance method itself:

# File: vendor/plugins/yaffle/test/acts_as_yaffle_test.rb

require File.dirname(__FILE__) + '/test_helper.rb'

class ActsAsYaffleTest < Test::Unit::TestCase

  def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
    assert_equal "last_squawk", Hickwall.yaffle_text_field
  end
  def test_a_hickwalls_yaffle_date_field_should_be_last_squawked_at
    assert_equal "last_squawked_at", Hickwall.yaffle_date_field
  end

  def test_a_wickwalls_yaffle_text_field_should_be_last_squawk
    assert_equal "last_tweet", Wickwall.yaffle_text_field
  end
  def test_a_wickwalls_yaffle_date_field_should_be_last_squawked_at
    assert_equal "last_tweeted_at", Wickwall.yaffle_date_field
  end

  def test_hickwalls_squawk_should_populate_last_squawk
    hickwall = Hickwall.new
    hickwall.squawk("Hello World")
    assert_equal "squawk! Hello World", hickwall.last_squawk
  end
  def test_hickwalls_squawk_should_populate_last_squawked_at
    hickwall = Hickwall.new
    hickwall.squawk("Hello World")
    assert_equal Date.today, hickwall.last_squawked_at
  end

  def test_wickwalls_squawk_should_populate_last_tweet
    wickwall = Wickwall.new
    wickwall.squawk("Hello World")
    assert_equal "squawk! Hello World", wickwall.last_tweet
  end
  def test_wickwalls_squawk_should_populate_last_tweeted_at
    wickwall = Wickwall.new
    wickwall.squawk("Hello World")
    assert_equal Date.today, wickwall.last_tweeted_at
  end
end

# File: vendor/plugins/yaffle/lib/acts_as_yaffle.rb

module Yaffle
  def self.included(base)
    base.send :extend, ClassMethods
  end

  module ClassMethods
    def acts_as_yaffle(options = {})
      cattr_accessor :yaffle_text_field, :yaffle_date_field
      self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
      self.yaffle_date_field = (options[:yaffle_date_field] || :last_squawked_at).to_s
      send :include, InstanceMethods
    end
  end

  module InstanceMethods
    def squawk(string)
      write_attribute(self.class.yaffle_text_field, string.to_squawk)
      write_attribute(self.class.yaffle_date_field, Date.today)
    end
  end
end

Note the use of write_attribute to write to the field in model.