gistfile1.rb

require 'test/unit'
require 'mocha/setup'
require 'fileutils'

class MyClass
  def do_it
    file = "/tmp/foo"
    FileUtils.touch(file)
    FileUtils.chmod(0777, file)
  end
end

class FooTest < Test::Unit::TestCase
  def test_it
    FileUtils.expects(:chmod).with(0777, '/tmp/foo')
    MyClass.new.do_it
  end
end