From: Devin Mullins <twifkak@...>
Date: 2005-06-08T22:56:52+09:00
Subject: Re: Test-Driven Development in GUIs

TDDing UI is hard, because it's a side-effect, rather than a return 
value or a parameter. I don't know the half of it. Nor, for that matter, 
know how to use Tk. I present to you a "Hello world" example.

require 'test/unit'

class Greeter
  def self.greet
    puts 'Hello, world!'
  end
end

class MockGreeter < Greeter
  class << self
    attr_reader :out
    def puts(*args)
      @out = @out ? [] : args
    end
  end
end

class TestGreeter < Test::Unit::TestCase
  def testGreet
    MockGreeter.greet
    assert_equal ['Hello, world!'], MockGreeter.out
  end
end

Subclass and override puts. Dependency injection doesn't help here. You 
can have greet take a Module as a parameter, and call module.puts, but 
you still need to test the container, and make sure it's passing Kernel 
to the greet method.

Sorry, that's the short version. I gotta go.

Devin