Rakefile

require 'rake/testtask'

Rake::TestTask.new('tester') do |t|
  t.test_files = 'test/*.rb'
end

testit.rb

require 'test/unit'

class Spacer
  def go
    puts namespace
  end

  def method_missing(*)
    puts 'ok'
  end
end

class TestIt < Test::Unit::TestCase
  def test_it
    Spacer.new.go
  end
end