.. an example of mocking gone too far.

config.rb

## configuration_spec.rb

require 'spec_helper'

describe Configuration do
  context "with the configuration variable set " do
    before do
      @config = Configuration.new(:key => 'hello', :value => 'goodbye')
      mock(Configuration).find_by_key('hello') { @config }
    end
        
    describe ".get" do
      it "should retrieve a configuration value" do
        Configuration.get('hello').should == 'goodbye'
      end
    end
    
    describe ".set" do
      it "should overwrite the old value" do
        mock(@config).save
        Configuration.set('hello', 'foo')
        @config.value.should == 'foo'
      end
    end
  end
  
  context "without the configuration variable set " do
    before do
      mock(Configuration).find_by_key('hello') { nil }
    end
    describe ".get" do
      it "should return nil" do
        Configuration.get('hello').should be nil
      end
    end
    
    describe ".set" do
      it "should create a new entry" do
        config = Configuration.new
        mock(config).save
        mock(Configuration).new(:key => 'hello') { config }
        Configuration.set('hello', 'foo')
        config.value.should == 'foo'
      end
    end
  end
  
end

## configuration.rb

class Configuration < ActiveRecord::Base
  def self.get key
    conf = find_by_key(key)
    conf ? conf.value : nil
  end
  
  def self.set key, val
    conf = find_by_key(key) || new(:key => key)
    conf.value = val
    conf.save
  end
    
end