main.rb

class Main

  def self.run
    b = Blah.new
    b.start
    b.stop
  end
  
end

main_spec.rb

require 'spec_helper.rb'
require 'main'

describe "main" do
  
  before do
    @blah = flexmock(:start => true, :stop => true)
    Blah = flexmock(:new => @blah)
  end
  
  it "should start blah" do
    @blah.should_receive(:start).and_return(true)
    Main.run
  end
  
  it "should start blah" do
    @blah.should_receive(:stop).and_return(true)
    Main.run
  end
  
  after do
    Object.send(:remove_const, :Blah)
  end
  
end

spec_helper.rb

begin
  require 'spec'
rescue LoadError
  require 'rubygems'
  gem 'rspec'
  require 'spec'
end

Spec::Runner.configure do |config|
  config.mock_with :flexmock
end