snippet.rb

class Array
  def delete_at_random l
    res = []
    l.times { res << delete_at(rand(size)) }
    res
  end
end

if __FILE__ == $0
  require "test/unit"

  class TestSomeModel < Test::Unit::TestCase
    def setup
      @array = (1..100).to_a
      @original = @array.dup
      @num = 5
    end
    
    def test_delete_at_random_gives_me_a_slice
      slice = @array.delete_at_random(@num)
      assert_instance_of(Array, slice)
      assert slice.all? { |e| @original.include? e }
    end
    
    def test_delete_at_random_deletes_result
      slice = @array.delete_at_random(@num)
      assert !slice.all? { |e| @array.include? e }
    end
    
  end
end