Avoid printing directly to stdout to make testing easier.

foo.rb

class Foo
  def bar(outstream)
    outstream.puts "BAZ"
  end
end

foo_spec.rb

$: << '.'
require 'foo'

describe Foo do
  let(:foo) { Foo.new }
  let(:outstream) { StringIO.new }

  it 'outputs bar' do
    foo.bar(outstream)
    outstream.string.should match(/baz/i)
  end
end

gistfile1.rb

#!/usr/bin/env ruby

$: << '.'
require 'foo'
foo = Foo.new
foo.bar(STDOUT)