You shoulda test your plugin!

So, lets assume you have a plugin "acts_as_teapot" that you want to include in some of your model classes. You've written a number of useful methods for teapot-like models to use, and now want to check that the models that are implementing acts_as_teapot actually are able to make use of the full spectrum of teapotly functionality.

You could write a set of asserts that you can tell your plugin's users to "please include these asserts/tests in your model classes"... but it's not DRY, and the users might miss one, and they'll get out of date real quick... what you want is kinda one big assert they can just put in once and that calls some library on the plugin itself (so it keeps up to date with the latest plugin code).

Luckily, shoulda is here to save the day! You can create a big context full of all the right tests and save it in the plugin file itself. This will be drawn in by the model at the time it's included. Then the user just has to call a single "shoulda" and it's all done for you.

Now, I was against shoulda for a long time - mainly wondering why anybody would use a half-arsed version of rSpec if they didn't actually want rSpec... but for me, plugin-testing is the killer-app that forced me to re-evaluate shoulda, and so far it actually looks ok. :)

So, to the code...

Plugin code

module Acts
  module Teapot
    def describe_me
      "short and stout"
    end
    def tip_me_over
      "pour me out"
    end
  end
end
class Test::Unit::TestCase
  def self.should_act_as_a_teapot
    klass = model_class

    context "A #{klass.name}" do
      setup { @new_klass = klass.new }

      should "respond to teapotly functions" do
        [:tip_me_over, :describe_me].each do |f|
          assert @new_klass.respond_to?(f), "#{klass.name} should respond to the function: #{f}"
        end
      end
      should "be short and stout" do
        assert_equal "short and stout", @new_klass.describe_me, "#{klass.name} is a funny-looking teapot."
      end
      should "pour me out" do
        assert_equal "pour me out", @new_klass.tip_me_over, "#{klass.name} doesn't make very good tea!."
      end
    end
  end
end

and testing the model:

class MyTeapot < ActiveRecord::Base
  acts_as_a_teapot
  #...
end

class MyTeapotTest < ActiveSupport::TestCase
  fixtures :my_teapots

  # plugin contexts
  should_act_as_a_teapot

end

There's a real-world example in the paperclip shoulda test