gistfile1.rb

# spec/helpers/application_helper_spec.rb
require 'spec_helper'

describe ApplicationHelper do
  
  describe "#logo" do
    it "image tag should point to logo.png" do
      helper.logo.should =~ /logo.png/i
    end
  end
end

# app/helpers/application_helper.rb
module ApplicationHelper 

  def logo
    if current_account && current_account.logo?
      image_tag(current_account.logo.url(:large), :alt => "Custom_Name")
    else
      image_tag("logo.png", :alt => "Name", :class => "round")
    end
  end
end

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
  protect_from_forgery
  helper_method :current_account

  def current_account
    # logic in here
  end      
end